Question

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 quarters does John have in his pocket?

Answer 1

By easy thinking - since the last digit is 0, he needs to have even quarters. 10 quarters is too much (in total, he would have over 2.50), 8 quarters is just enough (8 quarters are $2 + 5 dimes and it's $2.50)

Answer 2

so the answer is 8 qurarters right

Answer 3

yup

Answer 4

q + d = 13 --> d = 13 - q
.25q + .10d = 2.50

now sub 13 - q in for d in the 2nd equation
.25q + .10(13 - q) = 2.50
.25q + 1.30 - .10q = 2.50
.15q = 2.50 - 1.30
.15q = 1.20
q = 1.20/.15
q = 8

now sub 8 in for q in the 1st equation
q = d = 13
8 + d = 13
d = 13 - 8
d = 5

check...
.25q + .10d = 2.50
.25(8) + .10(5) = 2.50
2.00 + .50 = 2.50
2.50 = 2.50 (correct)

There are 8 quarters and 5 dimes