Question 393661
The total outing cost for a group of people amounted to Php. 8000. 
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Original DATA:
Let number in the group be "x".
Average cost per person is 8000/x Php.
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When an additional 4 persons decided to join the outing, the cost per person decreased by Php. 100.
New DATA:
Number in the group is "x+4".
Average cost perperson is 8000/(x+4) Php.
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How many people actually joined the outing?
Equation:
original average - new average = 100 Php
8000/x - 8000/(x+4) = 100
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Divide thru by 100 to get:
80/x - 80/(x+4) = 1
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Multiply thru by x(x+4) to get:
80(x+4) - 80x = x(x+4)
80*4 = x^2+4x
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x^2+4x-320 = 0
(x-16)(x+20) = 0
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Positive solution:
x = 16 (original # of people in the group)
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Cheers,
Stan H.