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Question

How many two-digit numbers have digits whose sum is a perfect square?

Choices...

A) 13
B) 16
C) 17
D) 18
E) 19

Answer 1

Well, what are the possibilities?
They could add up to 1, 4, 9, or 16.
There's only 1 way for the digits to add up to 1:
10
There's 4 ways for them to add up to 4:
13, 22, 31, 40
There's 9 ways for them to add up to 9:
18, 27, 36, 45, 54, 63, 72, 81, 90
And there's 3 ways for them to add up to 16:
79, 88, 97

1+4+9+3= 17

Answer 2

17

Answer 3

A) and D)