Posted by Rachel Kok on .
Tammy had 900 red and blue buttons in a big box. 30% of them were blue buttons . She sold some of the blue buttons in the afternoon and the percentage of blue buttons dropped to 25% . How many blue buttons were left

math 
PsyDAG,
X = number sold
.3(900)  x = .25(900x)
Solve for x and subtract from 900.