IMPLEMENTATION: Solve the system
xþy¼ 8
25 xþ 10 y¼ 125
Find the value ofy in the first equation. Substitute it in the second
equation and solve forx.
xþy¼ 8
xxþy¼ 8 x
y¼ 8 x
25 xþ 10 y¼ 125
25 xþ 10 ð 8 xÞ¼ 125
25 xþ 80 10 x¼ 125
15 xþ 80 ¼ 125
15 xþ 80 80 ¼ 125 80
15 x¼ 45
151 x
15
¼
45
15
x¼ 3
Findy:
xþy¼ 8
3 þy¼ 8
3 3 þy¼ 8 3
y¼ 5
Hence, there are 3 quarters and 5 dimes.
212 LESSON 18 Using Two Equations