Question

A number consist of two digits.The digit in tens place exceeds the unit digit place by 4.The sum of the digits is 1/7 of the number.The number is

Answer 1

let the unit digit be x
tens digit = x+4
$(x + 4 + x)7 = 10(x + 4) + x$
$14x + 28 = 11x + 40$
$3x = 12$
$x = 4$
number is 84