Question

In a two-digit number ,the digit at the units place is douale the digit in the tens place. The number exceeds the sum of digits by18.find the number.

Answer 1

n = 2 didit number

a = tens

b = ones

So:

n = 10 a + b

The number exceeds the sum of digits by18 mean:

n = a + b + 18

Now equalize exspressions for n.

n = n

10 a + b = a + b + 18

Subtract b to both sides

10 a + b - b = a + b + 18 - b

10 a = a + 18

Subtract a to both sides

10 a - a = a + 18 - a

9 a = 18

Divide both sides by 9

a = 18 / 9

a = 2

The digit at the units place is douale the digit in the tens place mean:

a = 2 b

this mean:

2 = 2 b

Divide both sides by 2

1 = b

b = 1

Your two-digit numer :

n = 21


Proof:

The number exceeds the sum of digits by18.

21 = 2 + 1 + 18

21 = 3 + 18

Answer 2

21