math
posted by petie .
DQ sells 6 times as many orders of french fries as sonic everyday. If both sold 60 more orders DQ would only sell 3 times as many fries. How many do each sell before and after the incease?
math  DrBob222, Wednesday, December 23, 2009 at 4:34pm
S = number FF Sonic sells.
D = number FF DQ sells.
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D = 6S every day.
If each sells 60 more, then
D + 60 = 3(S + 60) or
D + 60 = 3S + 120 or
D = 3S + 120
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The two equators are as follows:
D = 6S
D = 3S + 120
Solve these two simultaneous equation for D and S (before the addition of 60), then add 60 to each to determine the number sold after adding 60 to each. Post your work if you get stuck.
math  petie, Thursday, December 24, 2009 at 9:14am
Where did the 120 come from?

The 120 came from a multiplication error.
3(S + 60) = 3S +180
I hope this helps. 
PsyDAG is correct. I made two errors but they corrected each other; the final two final equations to solve simultaneously are correct.
If each sells 60 more, then
D + 60 = 3(S + 60) or
D + 60 = 3S + 120 or This should be
D + 60 = 3S + 180 which leads to
D = 3S + 120 and that is the same as the original. I was thinking faster than I was writing.
D = 3S + 120