Lauren P. answered 09/15/15
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I would set this up as two equations:
c = original cost per person
x = original number of people
so:
cx=120000
(c-6000)(x+1) = 120000
Solve the first equation for c and substitute in the second equation.
Once you do all the math and simplify, you will end up with a quadratic:
x2 + x - 20 = 0
(x-4)(x+5) = 0
so x = 4, -5
Have to eliminate -5 (there cannot be -5 people), so the answer is there were 4 people originally in the group.
To check this: 120,000/4 = 30,000.
Further: 120,000/5 = 24,000 which is a decrease per person of 6,000.