Question

Giselle works as a carpenter and as a blacksmith.
She earns
\[\$20\] per hour as a carpenter and
\[\$25\] per hour as a blacksmith. Last week, Giselle worked both jobs for a total of
\[30\] hours, and earned a total of
\[\$690\].
How long did Giselle work as a carpenter last week, and how long did she work as a blacksmith?

Answer 1

Let c = hours as a carpenter and b = hours as a blacksmith. Then
c + b = 30
20c + 25b = 690.

From the first, b = 30 − c. Substitute:
20c + 25(30 − c) = 690
20c + 750 − 25c = 690
−5c = −60, so c = 12.

Then b = 30 − 12 = 18.

Giselle worked 12 hours as a carpenter and 18 hours as a blacksmith.