Question 97153
The cashier's office at the college has collected $7020 from part-time students for a total of 42 courses. If each credit hour costs $45, how many 3-hour courses and how many 5-hour courses were paid for?
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Let # of 3-hr. courses be "x"; income from these is 3*45*x = 135x dollars
Let # of 5-hr. courses be "42-x" ; income is 5*45(42-x)=9450-225x dollars
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EQUATION:
income + income = 7020 dollars
135x + 9450-225x = 7020
-90x = -2430
x = 27 (# of 3-hr courses)
42-x = 15 (# of 5-hr courses) 
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Cheers,
Stan H.