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spnixon
#1 Posted : Thursday, July 12, 2018 10:01:03 PM
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For page 49 in the physics classroom companion, if we round 17 down to 16 and 0.24 to 0.25, isnt the denominator being estimated as lower than it really is, and so the actual number should be less than 625? Going by the answer in the back of the book, do we then assume that if we only round slightly, we are to pick the next closest number no matter if we rounded up or down?

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robertmoscaritolo
#2 Posted : Monday, July 23, 2018 6:36:32 PM
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Hello,

The product on the right-side of the equation was 17 x F x 0.24. As you’ve stated, the solution rounded 17 down to 16 and 0.24 up to 0.25. The overall effect of this rounding produces 16 x F x 0.25 = 4F. The denominator is then indeed less than it actually is, which will cause the rounded answer to be a bit larger than it actually is. This would imply that the rounded answer of 625 N is larger than it actually is. So, everything you have said is correct. However, on the left side of the equation, 2700 was rounded down to 2500. Since we rounded the numerator down by a lot more than we rounded the denominator, this implies that the rounded answer will be less than it actually is. So, the rounded answer of 625 N serves as a lower limit, telling us that the actual answer should be larger than 625 N, which is why D is the best choice. Please let me know if you nee any further clarification.

Robert Moscaritolo
MCAT Physics Instructor, Prep101
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