((-1.5)(1.2)-(4.5)(0.4))/30

Question

\frac{(-1.5)(1.2)-(4.5)(0.4)}{30}

(A) -1.2
(B) -0.12
(C) 0
(D) 0.12
(E) 1.2

b2bt · Accepted Answer

15*12 = 180 Shift two decimal left
45*4 = 180 Shift two decimal left
(- 1.8 - 1.8)/30 = -3.6/30 = -1.2/10 = -0.12

Answer is B
You only need to know that answer will be negative and eliminate C,D,E

arunspanda · Answer

\frac{(-1.5)(1.2)-(4.5)(0.4)}{30}

(A) -1.2
(B) -0.12
(C) 0
(D) 0.12
(E) 1.2

\frac{(-1.5)(1.2)-(4.5)(0.4)}{30}

=\frac{3((-0.5)(1.2)-(1.5)(0.4))}{30}

=\frac{(-6-6)}{10}

=\frac{-12}{10}

=-0.12

Answer:  (B)

Bunuel · Answer

SOLUTION

\frac{(-1.5)(1.2)-(4.5)(0.4)}{30}

(A) -1.2
(B) -0.12
(C) 0
(D) 0.12
(E) 1.2

\frac{(-1.5)(1.2)-(4.5)(0.4)}{30}=\frac{-1.8-1.8}{30}=\frac{-3.6}{30}=-0.12 .

Answer: B.

BrentGMATPrepNow · Answer

As always, scan the answers BEFORE solving the question. 
Here, the answer choices are VERY SPREAD APART, so we can be very aggressive with our estimation.

Aside: Some students might look at the answer choices and conclude that they are NOT very spread apart. After all, 1.12 is only 1.08 greater than 0.12
Instead, we need to examine their  relative  values. 
That is, 1.2 is TEN TIMES the value of 0.12
When we examine their relative values, we can conclude that they are very spread apart.

\frac{(-1.5)(1.2) - (4.5)(0.4)}{30} ≈\frac{ (-2)(1) - (4)(0.5)}{30}

≈ \frac{(-2) - 2}{30}

≈ \frac{-4}{30}

The closest answer is B

RELATED VIDEO
 https://www.youtube.com/watch?v=8GqcJGUVIk4

adkikani · Answer

niks18   pushpitkc   Abhishek009   pikolo2510   amanvermagmat

Can anyone explain below estimation step by  GMATPrepNow  :

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?

BrentGMATPrepNow · Answer

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, /30 ≈ 30 Does that help? Here's another question to practice with: https://gmatclub.com/forum/which-of-the ... 68916.html Cheers, Brent

JeffTargetTestPrep · Answer

Simplifying we have:

(-1.8 - 1.8)/30 = -3.6/30 = -36/300 = -0.12

Answer: B

5JUwiu4 · Answer

GMATPrepNow  ,

Could you elaborate on why these values are "very" spread apart? I can see from the equation the answer will be negative and with a little quick math you can see the number will be less than one, but my initial thought was not to estimate.

When you think about the "spread" of the answers are you thinking in just absolute magnitude or relative to each other. I.E. a question's "spread" with two answers: A:100 B=10 is equal to a questions with options A. .1 and B. .01?

Thanks

BrentGMATPrepNow · Answer

When I think about the "spread" of the answer choices, I'm talking about relative to each other. 
For example, the answer choices 0.01, 0.02, 0.04, 0.08 and 0.16 have a big spread, since each answer choice is TWICE the value of the answer choice before it. 
I consider this spread identical to the following answer choices: 3, 6, 12, 24 and 48

Cheers,
Brent

Paras96 · Answer

Observing the numeration, we can infer that the answer will be negative hence C,D,E eliminated.

Also there will be 2 decimals therefore answer A.

We can also solve to confirm.

Aboyhasnoname · Answer

Please tell me if what I did is risky, or this could be the right way to approach....

-1.5 x 1.12 approx -1.5.....-4.5 x 0.4..little less than half of 2.25......
equation comes (-1.5 - 2.25)/30 approx -3.75/30... -0.125 approx.....

I am always scared while doing approximations, its feels very risky...

totaltestprepNick · Answer

B https://www.youtube.com/watch?v=STlv9bdkmFY Nick Slavkovich, GMAT/GRE tutor with 20+ years of experience tutoring@totaltestprep.net

eeshajain · Answer

(−1.5)(1.2)−(4.5)(0.4)30=−1.8−1.830=−3.630=−0.12(−1.5)(1.2)−(4.5)(0.4)30=−1.8−1.830=−3.630=−0.12

Answer B

((-1.5)(1.2)-(4.5)(0.4))/30

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((-1.5)(1.2)-(4.5)(0.4))/30

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