Question

87. A student was asked to multiply a number by 12. But he multiplied by 21 and got his answer 72 more than the correct answer. The number to be multiplied was -
(a) 8
(b) 9
(c) 10
(d) 12​

Answer 1

Answer:

The number to be multiplied was 8.

Step-by-step explanation:

Let us assume:

The number to be multiplied be x.

The correct answer be y.

Given that:

A student was asked to multiply a number by 12.

⟶ x × 12 = y

⟶ y = 12x ______(i)

He multiplied by 21 and got his answer 72 more than the correct answer.

⟶ x × 21 = y + 72

⟶ 21x = y + 72

⟶ y = 21x - 72 ______(ii)

Finding the value of x:

Comparing eqⁿ(i) and eqⁿ(ii).

⇒ 12x = 21x - 72

⇒ 21x - 12x = 72

⇒ 9x = 72

⇒ x = 72/9

⇒ x = 8

∴ The value of x = 8

Answer 2

Step-by-step explanation:

Number to be multiplied= 12× x

number he multiplied= 21× x

which is 72 more

21×x-72= 12x

21x=12x+72

21x-12x= 24

7x-4x=24

3x= 24

x= 24/3= 8