Question

A farmer finds that he can buy 5 sheep and 5 cows for $129 or 10 sheep and 17 cows for $177.how much will it cost him to buy 3 sheeps and 2 cows?
Let s represent the sheep, and c represent the cows
5s + 5c = 129
10s + 17c = 177
Your choice is to use elimination or substitution to solve for c and s.
If you multiply 5s + 5c = 129 by -2 and then add it to the second equation it works out nicely and you can solve for c
-10s - 10c = -645
10s + 17c = 177
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7c = -645 + 177 and solve for c, then sub it back in to solve for s...
the answer is not correct b/c
5s + 5c = 129 when multiply by -2 it became

-10s - 10c = -258; not -10s - 10c = -645

finally c= -81/7

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