**Selina Concise Class 8 Math Chapter 21 Surface Area Volume and Capacity Exercise 21B Solution**

Concise Mathematics â€“ Class 8 Selina Exercise 21B Solution by experts | 21B Selina Concise Solution Class 8 | Class 8 Selina Concise Ex 21B Page 240 – 241 Solution | RK Bansal Class 8 ICSE Book Solution Online.

**(1) How many persons can be accommodated in a big-hall of dimensions 40 m, 25 m and 15 m assuming that each person requires 5 meter cube of air?**

**(2) The dimensions of a class-room are, length = 15 m, breadth = 12 m and a height = 7.5 m. Find, how many children can be accommodated in this class room, assuming 3.5 meter cube of air is needed for each child.**

**Solution: **

**(3) The length, breadth and height of a room are 6 m, 5.4 m and 4 m respectively. Find the area of (i) its four walls (ii) its roof.**

**(4) A room 5 m long , 4.5 m wide and 3.6 m high has one door 1.5 m by 2.4 m and two windows each 1 m by 0.75 m. Find:**

**(i) the area of its walls, excluding doors and windows.**

**(ii) the cost of distempering its walls at the rate of Rs. 4.50 per meter square.**

**(iii) the cost of painting its roof at the rate of Rs. 9 per meter square.**

**(5) The dining hall of a hotel is 75 m long, 60 m broad and 16 m high. It has five doors 4 m by 3 m each and four windows 3 m by 1.6 m each. Find the cost of:**

**(i) papering its walls at the rate of Rs. 12 per meter square.**

**(ii) carpeting its floor at the rate of Rs. 25 per meter square.**

**(6) Find the volume of wood required to make a closed box of external dimensions 80 cm, 75 cm and 60 cm, the thickness of walls of the box being 2 cm throughout.**

**Solution: **

**(7) A closed box measures 66 cm, 36 cm and 21 cm from outside. If its walls are made of metal sheet, 0.5 cm thick; find:**

**(i) the capacity of the box**

**(ii) volume of metal-sheet and**

**(iii) weight of the box, if 1 cm cube of metal weighs 3.6 g.**

**(8) The internal length, breadth and height of a closed box are 1 m, 80 cm and 25 cm respectively. If its sides are made of 2.5 cm thick wood; find: **

**(i) the capacity of the box**

**(ii) the volume of wood used to make the box.**

**(9) Find the area of metal-sheet required to make an open tank of length = 10 m, breadth = 7.5 m and depth = 3.8 m**

**Solution: **

**(10) A tank 30 m long, 24 m wide and 4.5 m deep is to be made. It is open from the top. Find the cost of iron-sheet required, at the rate of Rs. 65 per meter square. to make the tank.**

**Solution: **