Question 391887
Suppose the number is 10a + b, where a and b are digits. Then,


{{{a + b = (10a + b)/3}}}


{{{b = a + 5}}}. To make this an easy, single variable equation we replace all occurrences of b with a+5:


{{{a + (a+5) = (10a + (a+5))/3 = (11a + 5)/3}}}


{{{2a + 5 = (11a + 5)/3}}}


{{{6a + 15 = 11a + 5}}}


{{{a = 2}}} {{{b = 7}}}


The number is 27.