Solve forx:
xþy¼ 20
xþ 5 ¼ 20
xþ 5 5 ¼ 20 5
x¼15 pounds
Hence, 15 pounds of the $4 coffee are needed and 5 pounds of the $3 coffee
are needed.
EVALUATION: Check the second equation.
4 xþ 3 y¼ 20 ð 3 : 75 Þ
4 ð 15 Þþ 3 ð 5 Þ¼ 75
60 þ 15 ¼ 75
75 ¼ 75
EXAMPLE:A person has $5000 to invest and decides to invest part of it at
4% and the rest of it at 6^12 %. If the total interest for the year is $245, how
much does the person have invested at each rate?
SOLUTION:
GOAL: You are being asked to find the amounts of money invested at each
rate.
STRATEGY: Letx¼the amount of money invested at 4%
andy¼the amount of money invested at 6
1
2
%
Since the total amount of money is $5000, the first equation is
xþy¼$ 5000
218 LESSON 18 Using Two Equations