Question

The tens digit of a number is twice its ones digit . The sum of the number and that formed by reversing tthe digit is 99. Find the number.

Answer 1

Let us assume x is a tens digit and y is ones place digit are the two digits of a two digit number

Therefore, the number is 10x + y and reverse number is 10y + x

Given:

x = 2y --------1

Also given:

10x + y + 10y + x = 99

11x + 11y = 99

x + y = 9 -------------2

Substitute the value of x from equation 1 in equation 2

2y + y = 9

3y = 9

y = 3

Therefore, x = 2 * y = 2 * 3 = 6

Therefore, two digit number is = 10x + y = (10 * 6) + 3 = 63 

Answer 2

Answer:

Let the tens digit be y and the ones digit be x.

The original number = 10y + x

The reverse number = 10x + y

It is given that ones digit is twice the tens digit :]

➳ x = 2y ............[Equation (i)]

According to question now,

➳ 10x + y + 10y + x = 99

➳ 11x + 11y = 99

➳ 11 (x + y) = 99

➳ x + y = 99/11

➳ x + y = 9

➳ y = 9 - x.........[Equation (ii)]

Now, Substituting equation (ii) in equation (i) we get :

➳ x = 2 (9 - x)

➳ x = 18 - 2x

➳ 3x = 18

➳ x = 18/3

➳ x = 6

Putting x = 6 in equation (ii) we get :

➳ y = 9 - x

➳ y = 9 - 6

➳ y = 3

Therefore,

The original number = 10y + x = 10(3) + 6 = 30 + 6 = 36