This is from the GMAT800, page 246 Q5:
if x=3 and y=4, what is (xy)/(1/x + 1/y)
Plugging in the values you get:
12 / (1/3 + 1/4)
Since you can divide by multiplying by the inverse, I multiplied 12 by (3 + 4). (12 x (3/1 + 4/1)). This gives you 84.
This is wrong. The correct answer is to simplify the denominator first before doing that. You get 12 / (7/12), then multiply by the inverse gives you 144/7.
I understand the right answer completely, but I don't see where the error in reasoning lies in my original answer.
Thanks if anybody can point it out for me.
if x=3 and y=4, what is (xy)/(1/x + 1/y)
Plugging in the values you get:
12 / (1/3 + 1/4)
Since you can divide by multiplying by the inverse, I multiplied 12 by (3 + 4). (12 x (3/1 + 4/1)). This gives you 84.
This is wrong. The correct answer is to simplify the denominator first before doing that. You get 12 / (7/12), then multiply by the inverse gives you 144/7.
I understand the right answer completely, but I don't see where the error in reasoning lies in my original answer.
Thanks if anybody can point it out for me.
