word problem

Question

John has 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?

Answer 1

Let the number of quarters be q, and the number of dimes be d

 

   q     +     d = 13    (1)      (number of coins)

 

0.25q + 0.1d = 2.50  (2)      (value of coins)

 

2.5q    +   d  = 25    (3);    (2)*10

 

(3) - (1) ; 1.5q = 12 ; q = 12/1.5 = 8  (eliminating d)

 

from (1) d = 13 - q = 13 - 8 = 5  (substituting the value of q to get d)

 

There are 8 quarters and 5 dimes