John has a total of 13 coins in his pocket. Of the 13 coins, they are all either quarters or dimes. The total value of the coins is $2.50. How many dimes does John have in his pocket?

Question

curry · Answer

5 dimes

anonymous · Answer

put x = number of quarters  and therefore 13-x is number of dimes solve 
$$25x+10(13-x)=250$$ for x

anonymous · Answer

$$25x+130-10x=250$$
$$15x+130=250$$
$$15x=120$$
$$x=8$$ so 8 quarters. the rest are dimes

anonymous · Answer

If the following equation is used, then no follow on subtraction is required.
$$(13-x)(.25) +(x)(.10)=2.50$$