The sum of the digits of a two-digit number is twelve. If the units digit is thirteen less than four times the tens digit, find the number.

Answer 1

Well suppose the two digit number is ab

Then a + b = 12 (1)

b = 4a - 13 (2)

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So a + 4a - 13 = 12

5a - 13 = 12

5a = 25

a = 5

b = 4a-13 = 7

So the number is 57

You could also gave tried guess and check here

Using a+b= 12

a b 4a-13

1 11 Not possible, b >9

2 10 Not possible, b>9

3 9 -1

4 8 8

5 7 7

6 6 11

7 5 15

8 4 19

9 3 23