## Selina Concise Mathematics Class 6 ICSE Solutions Chapter 20 Substitution (Including Use of Brackets as Grouping Symbols)

**Selina Publishers Concise Mathematics Class 6 ICSE Solutions Chapter 20 Substitution (Including Use of Brackets as Grouping Symbols)**

### Substitution Exercise 20A – Selina Concise Mathematics Class 6 ICSE Solutions

Question 1.

Fill in the following blanks, when :

x = 3,y = 6, z = 18, a = 2, b = 8, c = 32 and d = 0.

Solution:

Question 2.

Find the value of :

Solution:

Question 3.

Find the value of :

Solution:

Question 4.

If a = 3, b = 0, c = 2 and d = 1, find the value of :

Solution:

Question 5.

Find the value of 5x^{2} – 3x + 2, when x = 2.

Solution:

Question 6.

Find the value of 3x^{3} – 4x^{2} + 5x – 6, when x = -1.

Solution:

Question 7.

Show that the value of x^{3} – 8x^{2} + 12x – 5 is zero, when x = 1.

Solution:

Question 8.

State true and false :

(i) The value of x + 5 = 6, when x = 1

(ii) The value of 2x – 3 = 1, when x = 0

(iii) \(\frac { 2x-4 }{ x+1 }\) = -1,when x = 1

Solution:

Question 9.

If x = 2, y = 5 and z = 4, find the value of each of the following :

Solution:

Question 10.

If a = 3, find the values of a^{2} and 2^{a}.

Solution:

Question 11.

If m = 2, find the difference between the values of 4m^{3} and 3m^{4}.

Solution:

### Substitution Exercise 20B – Selina Concise Mathematics Class 6 ICSE Solutions

Question 1.

Evaluate :

(i) (23 – 15) + 4

(ii) 5x + (3x + 7x)

(iii) 6m – (4m – m)

(iv) (9a – 3a) + 4a

(v) 35b – (16b + 9b)

(vi) (3y + 8y) – 5y

Solution:

Question 2.

Simplify :

Solution:

Question 3.

Simplify :

Solution:

### Substitution Exercise 20C – Selina Concise Mathematics Class 6 ICSE Solutions

Question 1.

Fill in the blanks :

Solution:

Question 2.

Insert the bracket as indicated :

Solution:

### Substitution Revision Exercise – Selina Concise Mathematics Class 6 ICSE Solutions

Question 1.

Find the value of 3ab + 10bc – 2abc when a = 2, b = 5 and c = 8.

Solution:

Question 2.

If x = 2, y = 3 and z = 4, find the value of 3x^{2} – 4y^{2} + 2z^{2}.

Solution:

Question 3.

If x = 3, y = 2 and z = 1; find the value of:

(i) x^{y}

(ii) y^{x}

(iii) 3x^{2} – 5y^{2}

(iv) 2x – 3y + 4z + 5

(v) y^{2} – x^{2} + 6z^{2}

(vi) xy + y^{2}z – 4zx

Solution:

Question 4.

If P = -12x^{2} – 10xy + 5y^{2}, Q = 7x^{2} + 6xy + 2y^{2}, and R = 5x^{2} + 2xy + 4y^{2} ; find :

(i) P – Q

(ii) Q + P

(iii) P – Q + R

(iv) P + Q + R

Solution:

Question 5.

If x = a^{2} – bc, y = b^{2} – ca and z = c^{2} – ab ; find the value of :

(i) ax + by + cz

(ii) ay – bx + cz

Solution:

Question 6.

Multiply and then evaluate :

(i) (4x + y) and (x – 2y); when x = 2 and y = 1.

(ii) (x^{2} – y) and (xy – y^{2}); when x = 1 and y = 2.

(iii) (x – 2y + z) and (x – 3z); when x = -2, y = -1 and z = 1.

Solution:

Question 7.

Simplify :

(i) 5 (x + 3y) – 2 (3x – 4y)

(ii) 3x – 8 (5x – 10)

(iii) 6 {3x – 8 (5x – 10)}

(iv) 3x – 6 {3x – 8 (5x – 10)}

(v) 2 (3x^{2} – 4x – 8) – (3 – 5x – 2x^{2})

(vi) 8x – (3x – \(\bar { 2x-3 }\))

(vii) 12x^{2} – (7x – \(\bar { 3x^{ 2 }+15 }\))

Solution:

Question 8.

If x = -3, find the value of : 2x^{3} + 8x^{2} – 15.

Solution: