Edudel, Directorate of Education Govt. of NCT of Delhi Class 6 Mental Maths Chapter 1 Knowing our Numbers Questions Solution. In this chapter, there is total 40 math problems. We have given each questions solution step by step.
1.) Make the greatest 5-digit number, using the digits 6, 2,5,8,4 only once.
Answer: As 8 is greater than 6,5,4,2 and 6 is greater than 5,4,2 and 5 is greater than 4,2 and 4 is greater than 2
we keep all mentioned number in descending order to get highest number
And we get the greatest 5-digit number = 86542
2.) Find the product of the place value of two 3’s in 534370.
Answer:
The place value of 3 in 534370 is
30000 and 300.
The product value of two 3’s in 534370 =
30000 × 300
= 9000000
Therefore The product value of two 3’s in 534370 is 9000000
3.) Make the smallest 5 -digit number, using the digits 7, 9,3,8,5 only once.
Answer:
As 3 is smaller than 5,7,8,9 and 5 is smaller than 7,8,9and7 is smaller than 8,9 and 8 is smaller than 9
We keep all mentioned number in ascending order to get smallest number
And we get the smallest 5-digit number = 35789
4.) Find the sum of the place values of two 5’s in 75450.
Answer:
The place value of 5 in 75450 is
5000 and 50
The Sum of the place values of two 5’s in 75450
= 5000 + 50
= 5050
Therefore, The Sum of the place values of two 5’s in 75450 is 5050
5.) Find the value of:45 × (14 ˗ 9)
Answer :
The value of 45 × (14-9)
= 45 × 5
= 225
The value of 45 × (14-9) = 225
6.) Write 24 in Roman numerals.
Answer :
Roman Numerals are expressed by letters of the English alphabet.
M(1,000), D(500), C(100), L(50), X(10), V(5), I(1)
The number 24 means 10 + 10 + 4
We can write this expanded version of 24 = 10 + 10 + 4
In Roman Numerals we can express it as = 10 (X) + 10(X) + 4(IV)
Therefore The 24 in Roman numerals is written as XXIV
7.) How many thousands are there in two lakhs?
Answer: Two lakhs i.e 200,000
200,000 can also be said as Two Hundred Thousand
Therefore we can say there is 200 thousands in Two lakhs
8.) Find the value of: 80 + (15 × 4)
Answer:first solve the bracket
We get
=80+ (60)
= 140
Therefore, The value of 80 + (15×4) is 140
9.) A student Ajit’s height is 1m 29 cm. Find his height in cm.
Answer :
Ajit’s height is 1m 29 cm
We need to find Ajit’s height only in cm
We know 1 meter = 100 centimeter
So Ajit’s height in cm = 100 cm + 29 cm
= 129 cm
Therefore, Ajit’s height in cm is 129 cm
10.) Find the number: 7 ×10000 + 5 ×1000 + 4 × 100 + 8 × 10.
Answer: Solving the above question , we need to follow the BODMAS rule ieB – Brackets, O – Order of powers or roots, D – Division, M – Multiplication A – Addition, and S – Subtraction.
As per the BODMAS rule ,
first solve the multiplication and then addition
The number we get is
=(7×10000) + (5×1000) + (4×100) + (8×10)
=70000 + 5000 + 400 + 80
= 75480
Therefore The number we get Solving 7 ×10000 + 5 ×1000 + 4 × 100 + 8 × 10 is 75480
11.) Find the difference between smallest 4 -digit number and largest 4 -digit number.
Answer :
Largest 4- digit number is 9,999
Smallest 4- digit number is 1,000
The difference between smallest 4 -digit number and largest 4 -digit number = 9,999 – 1,000
= 8,999
12.) How many seconds make 7 minutes?
Answer:
1 minute = 60 seconds
So 7 minutes = (60 × 7) seconds
7 minutes = 420 seconds
Therefore 420 seconds make 7 minutes
13.) Simplify: 48 + 5 × 4 –(24 + 6) – 7
Answer :-
As per the BODMAS rule
First solve the bracket then multiplication, addition and then Subtraction
And we get
= 48 + 5 × 4 –(30) – 7 – – – – – – (bracket solved)
=48 + (5 × 4) – (30) – 7
= (48 + 20)– 30 – 7 – – – – – – (multiplication solved)
= 68 – 30 – 7 – – – – – – (Addition solved)
= 31
Therefore simplifying 48 + 5 × 4 –(24 + 6) – 7 we get 31
14.) How many metres should be added to 24 km 450m to make 30 km 550m?
Answer :
Let the meter to be added in 24km 450m be X
24km 450m + X = 30km 550m – – – – – – (equation 1)
We need to find the value of X
1km = 1000m
Convert km into m
24km 450 m = (24000 + 450) m
24km 450 m = 24450 m
30km 550 m = (30000 + 550) m
30km 550 m = 30550 m
We can write equation 1 in meters as
24450 + X = 30550
X = 30550 – 24450
X = 6100
Therefore the meter to be added in 24km 450m to make 30 km 550m is 6100 m
15.) Ravi had Rs 75500. He gave Rs5350 to Garima and Rs 15,150 to Ramesh. How much money is left with Ravi?
Answer :
Money Ravi had = Rs 75500
Money Ravi gave to Garima = Rs 5350
Money Ravi gave to Ramesh = Rs 15150
Need to find money left with Ravi
Money left with Ravi = Rs ( 75500 – 5350 – 15150)
Money left with Ravi = Rs55000
Therefore Rs 55000 money is left with Ravi
16.) Prakash buys 10 notebooks and 20 pens. If the cost of one notebook is Rs35 and cost of one pen be Rs10, how much money did he spend?
Answer:
Prakash buys 10 notebooks and 20 pens
If cost of 1 notebook is Rs 35
And cost of 1 pen in Rs 10
Total money spend will be
Cost of 10 notebooks in Rs= 10 × 35
= 350 Rs
Cost of 20 pens in Rs = 20 × 10
= 200 Rs
Total money spend by Prakash = cost of 10 notebooks + cost of 20 pens
Total money spend by Prakash= (350 + 200) Rs
Total money spend by Prakash= 550 Rs
Therefore Rs 550 money have Prakash spend.
17.) Find the sum of smallest 3 – digit number and largest 4 -digit number.
Answer:
Largest 4- digit number is 9999
Smallest 3- digit number is 100
The sum of smallest 3-digit number and largest 4 -digit number = 9999 + 100
= 10099
18.) How many milliliters make a liter?
Answer : 1 liter = 1000 milliliters
Therefore 1000 milliliters make a liter
19.) How many centimetres make 18 metres?
Answer: 1 meter = 100 centimetres
18 meters = 18 × 100 centimetres
18 meters = 1800 centimetres
Therefore 1800 centimetres make 18 meters
20.) A box contains 40000 toffees, each toffee weighs 5gm .What is the total weight of the box in kg?
Answer:
No. Of toffees 1 box contains = 40000
1 toffee weighs in gm = 5 gm
1 Toffee weighs in kg = 0.005 kg – – – – – ( 1kg = 1000 gm)
Total weigh of the box in kg = Total no. Of toffees in 1 boxx weigh of 1 toffee
Total weigh of the box in kg = (40000 x 0.005)
Total weigh of the box in kg = 200
Therefore the total weigh of the box is 200 kg
21.) There are 48 pages in a notebook. How many pages are there in 20 such notebooks?
Answer:
1 notebook contain = 48 pages
20 notebooks contains = 48 × 20
20 notebooks contains = 960 pages
Therefore 960 pages are there in 20 such notebooks
22.) Arrange in ascending order:- 4379, 4739, 4397, 4793
Answer :
All the 4 numbers are in thousands
Ascending order is followed from left to right with smallest to largest value
All the numbers has 4 common digit in thousands place
Check and consider with hundred place value and then tens and lastly unit place value
We get ascending order as
4379 and 4397 smaller than remaining number
Now comparing the tens place value
we get ascending order as 4379 < 4397
Similarly compare remaining numbers
We get
4379 < 4397 < 4739 < 4793
23.) Arrange in descending order:- 43251, 43521, 43125, 43152
Answer: Descending order is followed from left to right with largest to smallest value
All the numbers has 43 common digit in thousands place
Check and consider with hundred place value and then tens and lastly unit place value
Comparing hundreds and tens place value we get descending order as
43521 >43251 > 43152 > 43125
24.) Arrange in ascending order :- 27643, 26743, 27634, 24736
Answer:
Ascending order is followed from left to right with smallest to largest value
Check and consider with thousands , hundred place value and then tens and lastly unit place value
Comparing thousands, hundreds and tens place value we get ascending order as
24736<26743<27634<27643
25.) Arrange in descending order :- 1548, 1584, 1854, 1845
Answer :
Descending order is followed from left to right with largest to smallest value
Check and consider with thousands , hundred place value and then tens and lastly unit place value
Comparing thousands, hundredsand tens place value we get descending order as
1854 > 1845 > 1584 >1548
26.) Make the largest 4-digit number using the digits 3,5,7,0.
Answer :As 7 is greater than 5,3,0 and 5 is greater than 3,0 and3 is greater than 0
we keep all mentioned number in ascending order to get highest number
We get the largest 4- digit number using the digits 3,5,7,0 is 7530
27.) Take two digits 0 and 1. Make the greatest 4 -digit number using both the digits equal number of times.
Answer :
4 -digit number that forms using 0 and 1 digits with equal number of times = 1001, 1010, 1100
The greatest number from above numbers is 1100
The greatest 4 -digit number using 0 and 1 digits with equal number of times will be 1100
28.) Take two digits 0 and 1. Make the smallest 4 -digit number using both the digits equal number of times.
Answer :
4 -digit number that forms using 0 and 1 digits with equal number of times = 1001, 1010, 1100
The smallest number from above numbers is 1001
The smallest 4 -digit number using 0 and 1 digits with equal number of times will be 1001
29.) Write in Roman numerals :80
Answer:
Roman Numerals are expressed by letters of the English alphabet.
M(1,000), D(500), C(100), L(50), X(10), V(5), I(1)
The number 80 means 50+10 + 10 + 10
In Roman number 80 = LXXX
Therefore Roman numerals of 80 is LXXX
30.) The monthly salary of Rohit is Rs 20975 and that of Reena is Rs 15875. What is the difference between their monthly salaries?
Answer:
Monthly salary of Rohit is Rs 20975
Monthly salary of Reena is Rs 15875
Difference between Rohit and Reena monthly salaries is
(Monthly salary of Rohit – Monthly salary of Reena)
Difference between their monthly salaries is Rs (20975 – 15875)
Difference between their monthly salaries is = Rs 5100 /-
Therefore Rs 5100 /- is the difference between their monthly salaries
31.) Manish multiplied 100 by 89 instead of multiplying by 79 .How much was his answer greater than the correct answer?
Answer :
Manish was suppose to multiple 100 by 79
Answer Manish was suppose to get is 100 × 79 = 7900
In actual Manish multiplied 100 by 89
The answer Manish got is 100 × 89 = 8900
Difference in the answer Manish got is (8900 – 7900)
= 1000
1000 was Manish answer greater than the correct answer
32.) Sangeeta types 25 pages per day. How many pages will she type in the month of November?
Answer :
Per day (1 day) no. Of pages Sangeeta types= 25
Month of November no. Of pages Sangeeta will type =
( No. Of days in November × No. Of pages type in 1 day )
= 30 × 25
= 750 pages
Therefore 750 pages will Sangeeta type in the month of November
33.) How many times the digit 0 comes in 10 crores?
Answer : 10 crores= 10,00,00,000 in numbers
Therefore 8 times the digit 0 comes in 10 crores
34.) Anita’s age is 48 years. How is her age represented in Roman system?
Answer :
Roman Numerals are expressed by letters of the English alphabet.
M(1,000), D(500), C(100), L(50), X(10), V(5), I(1)
In number system Age of Anita is 48 years
In Roman system age of Anita is = ( 50 – 10 + 5 + 1 + 1 +1)
= XLVIII
Or using Roman Numeral Chart
In Roman system age of Anita is = 40 + 8
= (XL + VIII)
= XLVIII
Therefore In Roman system age of Anita isXLVIII
35.) How many numbers are there containing 3 – digits?
Answer:
Largest Numbers containing the 3- digit number = 999
Smallest number containing the 3- digit number = 100
The Numbers that are there containing 3 – digits = Difference between largest 3-digit number and smallest 3-digit number
The Numbers that are there containing 3 – digits = 999- 100
The Numbers that are there containing 3 – digits = 900
36.) The estimated value of 5784 – 437 is?
Answer:
37.) Write the number for the expanded form :- 2 × 10000 + 8 × 10 + 5 × 1
Answer :
As per BODMAS rule
We get
2 × 10000 + 8 × 10 + 5 × 1 = (2×1000) + (8×10) + (5×1) – – – ( first solve multiplication)
= 20000 + 80 + 5- – – – – ( Solve addition )
= 20085
The number for the expanded form :- 2 × 10000 + 8 × 10 + 5 × 1 is 20085
38.) The distance between Delhi and Agra is 233 km. What is the distance in metres?
Answer : Distance between Delhi and Agra in km is 233 km
1 km = 1000 m
Convert 233km in metres by multiplying 233 by 1000
Distance between Delhi and Agra in m = (233 × 1000)
Distance between Delhi and Agra in m = 233000 m
39.) Keeping the place of 5 unchanged in the number 537068, find the smallest number obtained by rearranging other digits.
Answer: The number given is 537068
Place value 5 in the given number is kept unchanged ie500000
Now rearranging the rest/ remaining number in such the way to get smallest number
Remaining numbers are 37068
Now arrange the number in ascending order we get03678
The smallest number obtained by rearranging other digits is 503678
40.) Estimate the quotient to the nearest tens: 74 divided by 8.
Answer:74 divided by 8 = 74 ÷ 8
= 9.25
The quotient is 9.25
As 6, 7, 8, 9 are numbers nearer to 10 than 0, so they are rounded off to 10.
The quotient to the nearest tens is10