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Mary had equal number of green, yellow and red tokens. She used some of those tokens to make a pile. You can see all used tokens in the figure. She still has five tokens which are not on the pile. How many yellow tokens did she have have at the beginning?  insert pic 
Overseas Competition->Knowledge Point->Counting Modules->Counting the Number of Figures->Counting Solid Figures
The used tokens are 5 red tokens at the bottom, 4 green tokens and 4 yellow tokens. Now we distribute the unused 5 tokens to the 3 colors such that each color has the same number of tokens.  Firstly, we need 1 more green token and 1 more yellow token to make all colors equal in number of tokens.  We are left with 3 tokens, and we will equally distribute these tokens to the colors, i.e. each color will have 1 more token.  Hence, the unused tokens are 1 red, 2 green and 2 yellow. There are 4+2 = 6 yellow tokens in total. 