Question 143386
A math class planned a field trip to a computer center. The trip cost $240 to be paid equally by each student. 4 students suddenly can't go. This increased the cost by $2 per student. How many students went to the computer center? 
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Let original number in class be "x"
Total cost for the group was 240x dollars
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Average cost when 4 cannot go : 240x/(x-4)
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EQUATION:
new average - old average = 2 dollars
240x/(x-4) - 240 = 2
240x/(x-4) = 242
240x = 242x - 968
2x = 968
x = 484 (# of students who planned to go to the computer center)
x-4 = 480 (# of students who actually went)
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Cheers,
Stan H.