SOLUTION: Sierra has fifteen fewer pennies than quarters. Sierra has a total of 25 pennies and quarters. How much money does she have?

1.  "Sierra has fifteen fewer pennies than quarters."  ====>  P = Q - 15
     where P = the number of pennies, and Q = the number of quarters.


2.  "Sierra has a total of 25 pennies and quarters."  ====>  P + Q = 25.


You have two equations:

P = Q - 15,   (1)   and
P + Q = 25.   (2)

From (1), substitute the expression P = Q-15 into (2), replacing P. You will get

(Q-15) + Q = 25.

Simplify and solve 

2Q - 15 = 25,

2Q = 25 + 15,

2Q = 40  ====>  Q =  = 20.

The number of quarters is 20.

Hence, the number of pennies is 25-20 = 5.


Answer. 5 pennies and 20 quarters.