Question

The value of a two-digit number is 10 more than 3 times the sum of its digits. The units digit is 1 more than twice the tens digit. What is the two-digit number?

Answer 1

49

Explanation:

the number is "ab" (2 digits).

ab - 10 = 3×(a+b)

a number is actually the sum of multiplying the digits with their associated powers of 10.

a×10 + b - 10 = 3a + 3b

7a - 2b = 10

b-1 = 2×a

b = 2a + 1

7a - 2×(2a+1) = 10

7a - 4a - 2 = 10

3a = 12

a = 4

b = 2×4 + 1 = 9