Renee has 16 coins in her pocket. She only has nickels and dimes. Her coins total $1.20. How many nickels and how many dimes did she have in her pocket.

Question

Substitution 

Answer 1

n = #nickels

d = #dimes

 

there are 16 coins:

 

n + d = 16 ________ eqn 1

 

Total money is $1.20:

 

.05n + .1d = 1.20 __ eqn 2

 

from eqn 1 solve for n and substitute

into eqn 2

 

n = 16-d

 

.05(16-d) + .1d = 1.20

.8 - .05d + .1d = 1.20

.05d = .40

d = .40/.05

d = 8 dimes

n = 16-8 = 8 nickels

 

check:  8(.1) + 8(.05)

         = .8 + .4

         = $1.20