7 7 þy¼ 15 7
y¼ 8
Hence, the number is 78.
EVALUATION: Check the information in the second equation.
Original number¼ 78
Reversed number¼ 87
Since 87 is 9 more than 78, the answer is correct.
EXAMPLE:A person has 8 coins consisting of quarters and dimes. If the
total amount of this change is $1.25, how many of each kind of coin are
there?
SOLUTION:
GOAL: You are being asked to find how many coins are quarters and how
many coins are dimes.
STRATEGY: Letx¼the number of quarters
y¼the number of dimes
25 x¼the value of the quarters
and 10y¼the value of the dimes
Since there are 8 coins, the first equation is
xþy¼ 8
Since the total values of the quarters plus the dimes is $1.25 or 125c, the
second equation is
25 xþ 10 y¼ 125
LESSON 18 Using Two Equations 211