Selina Concise Class 6 Math Chapter 18 Substitution Exercise 18B Solution
EXERCISE 18B
(1) Evaluate:
(i) (23 – 15) + 4
= 8 + 4
= 12
(ii) 5x + (3x+ 7x)
= 5x + 10x
= 15x
(iii) 6m – (4m – m)
= 6m – 3m
= 3m
(iv) (9a – 3a) + 4a
= 6a + 4a
= 10a
(v) 35b – (16b + 9b)
= 35b – 25b
= 10b
(vi) (3y + 8y) – 5y
= 11y – 5y
= 6y
(2) Simplify:
(i) 12x – (5x + 2x)
= 12x – 7x
= 5x
(ii) 10m + (4n – 3n) – 5n
= 10m + n – 5n
=10m – 4n
(iii) (15b – 6b) – (8b + 4b)
= 9b – 12b
= – 3b
(iv) – (- 4a – 8a)
= – (- 12a)
= 12a
(v) x – (x – y) – (- x + y)
= x – x + y + x – y
= x
(vi) p + (- q – r – s) – (p – q – r)
= p – q – r – s – p + q + r
= – s
(vii) (a + b) – (c + d) – (e – f)
= a + b – c – d – e + f
(viii) 3x + (8x – 5x) – (7x – x)
= 3x + 8x – 5x – 7x + x
= (3x + 8x + x) – (5x + 7x)
= 12x – 12x
= 0
(ix) a – (a – b – c)
= a – a + b + c
= b + c
(x) 6a2 + (2a2 – a2) – (a2 – b2)
= 6a2 + 2a2 – a2 – a2 + b2
= (6a2 + 2a2) – (a2 + a2) + b2
= 8a2 – 2a2 + b2
= 6a2 + b2
(xi) 2m – (3m + 2n – 6n)
= 2m – 3m – 2n + 6n
= – m + 4n
= 4n – m
(xii) – m – n – (- m) – m
= – m – n + m – m
= – n – m
(xiv) 25y – (5x – 10y + 6x – 3y)
= 25y – 5x + 10y – 6x + 3y
= (25y + 10y + 3y) – 5x – 6x
= 38y – 11x
= – y + x – (- x)
= – y + x + x
= 2x – y
(3) Simplify:
(i) x – (y – z) + x + (y – z) + y – (z + x)
= x – y + z + x + y – z + y – z – x
= (x + x – x) – y + y + y + z – z – z
= x + y – z
(ii) x – [y + {x – (y + x)}]
= x – [y + {x – y – x}]
= x – [y + x – y – x]
= x – y – x + y + x
= x – x + x – y + y
= x
(iii) 4x + 3 (2x – 5y)
= 4x + 6x – 15y
= 10x – 15y
(iv) 2(3a – b) – 5(a – 3b)
= 6a – 2b – 5a + 15b
= 6a – 5a – 2b + 15b
= a + 13b
(vii) 3x – [5y – {6y + 2 (10y – x)}]
= 3x – [5y – {6y + 20y – 2x}]
= 3.x – [5y – 26y + 2x]
= 3x – [- 21y + 2x]
= 3x + 21y – 2x
= x + 21y