Question 288255
I don't see what you're doing wrong. I got the same answer (12/7, or 1 and 5/7) through a similar method:
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Rate of A: 1/3
Rate of B: 1/4
Time working together: x
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The equation would then be:
x/3 + x/4 = 1
(4x + 3x)/12=1
7x=12
<b>x=12/7</b>
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You multiplied both sides to get rid of the divisor (12), I assume... Although I think an easier way would've been to simply move 12 to the expression on the right of the equation, turning the divisor into a multiplier (as I have done).
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You might want to consider the possibility of the book rounding up the answer to the nearest hour (which is indeed "2"). Hope this helps.