EVALUATION: Find the values of each and see if their sum is $1.25.
3 quarters¼ 3 $ 0 : 25 ¼$ 0 : 75
5 dimes¼ 5 $ 0 : 10 ¼$ 0 : 50
$ 0 : 75 þ$ 0 : 50 ¼$ 1 : 25
EXAMPLE:Bill is 8 years older than his brother. In 3 years, Bill will be twice
as old as his brother. Find their present ages.
SOLUTION:
GOAL: You are being asked to find the present ages of Bill and his brother.
STRATEGY: Let x¼Bill’s age
y¼his brother’s age
xþ 3 ¼Bill’s age in 3 years
yþ 3 ¼his brother’s age in 3 years
Since Bill is 8 years older than his brother, the first equation is
x¼yþ 8
In 3 years, Bill will be twice as old as his brother, so the second equation
is
xþ 3 ¼ 2 ðyþ 3 Þ
IMPLEMENTATION: Solve the system
x¼yþ 8
xþ 3 ¼ 2 ðyþ 3 Þ
LESSON 18 Using Two Equations 213