Problem
First name
fifi
School
Tetherdown
Country
Age
10
Email address
12motero@gmail.com
For the question "What is the smallest number that belongs in all four sets?" the answer would be 210. How to solve it:
Triangular numbers that are multiples of 5:
10
15
45
55
105
120
190
210 ...
Even numbers (but not multiples of 4) that are also triangular numbers and multiples of five:
10
190
210 ...
And the multiple of 3 (and not of nine) is 210!!!! And because it is the smallest possible number, it is the answer to this question.