Mary buys 100 candies for $7. If yips cost 5 cents each, Gups 6 cents each and pips 7 cents each, how many more pips than yips did Mary buy?
A 50 B 60 C 70 D 100 E none of the above
Let y denote the number of yips, g the number of gups and p the number of pips.
From the text of the question you know:
$\displaystyle y+g+p=100$
$\displaystyle 0.05y+0.06g+0.07p=7~\implies~5y+6g+7p=700$
Multiply the first equation by 6 and subtract both equations columnwise to get rid of the gups. Solve for y.