adkikani wrote:
niks18 pushpitkc Abhishek009 pikolo2510 amanvermagmatCan anyone explain below estimation step by
GMATPrepNow :
Quote:
[(-1.5)(1.2) - (4.5)(0.4)]/30 ≈ [(-2)(1) - (4)(0.5)]/30
Here is how I proceeded:
I knew 15*12 = 180 and hence shifted decimals though this is prone to error,
finally -1.8 approximated to -2
For 4.5* 0.4 I converted it in to fractions: (45/10) * (4/10) ie 18/10
finally 1.8 approximated to 2.0
Did Brent in highlighted text approximated 0.4 to 0.5 since 0.5 ie 1/2 is easier to multiply with fractions?
But then can we simply deduct 0.1 from 4.5 ??
He deducted 0.1 from 4.5 and added 0.1 to 0.5, I suppose but is this a valid mathematical step?
The key here is that the answer choices are quite spread apart, which means
we can replace values with other values that are reasonably close.
So, for example, we can replace -1.5 with -2 (close enough!)
We can replace 1.2 with 1
We can replace 4.5 with 4
And we can replace 0.4 with 0.5
So, [(-1.5)(1.2) - (4.5)(0.4)]/30 ≈ [(-2)(1) - (4)(0.5)]30
Does that help?
Here's another question to practice with:
https://gmatclub.com/forum/which-of-the ... 68916.htmlCheers,
Brent