Answers

2016-07-13T21:04:40+08:00
The numbers between are 3, 6, 9, ... , 99

3 + 6 + ... + 99
= 3 (1 + 2 + ... + 33)
= 3 * 33 * 34 ÷ 2
= 99 * 17
= 1683
0