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15 Oct 2018, 08:03
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A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
96% (00:54) correct
4%
(00:53)
wrong
based on 89
sessions
History
Date
Time
Result
Not Attempted Yet
What is the area of the equilateral triangle if the base BC = 6?
(A) \(9 \sqrt{3}\)
(B) \(18 \sqrt{3}\)
(C) \(26 \sqrt{3}\)
(D) \(30 \sqrt{3}\)
(E) \(36 \sqrt{3}\)
Attachment:
triangle (1).jpg [ 9.13 KiB | Viewed 3654 times ]
Updated on: 27 Apr 2021, 16:48
Originally posted by BrentGMATPrepNow on 15 Oct 2018, 08:14.
Last edited by BrentGMATPrepNow on 27 Apr 2021, 16:48, edited 1 time in total.
Last edited by BrentGMATPrepNow on 27 Apr 2021, 16:48, edited 1 time in total.
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Bunuel
Useful formula: Area of equilateral triangle = (side²)(√3)/4
In this question, we're told that each side has length 6.
So, area = (6²)(√3)/4
= (36)(√3)/4
= 9√3
Answer: A
RELATED VIDEO
15 Oct 2018, 08:26
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Bunuel
A different approach....
IMPORTANT: the diagrams in GMAT problem solving questions are DRAWN TO SCALE unless stated otherwise.
So, we can assume that the above diagram IS drawn to scale.
This means we may be able to solve the question by simply "eyeballing" the diagram.
We know that the area of a triangle = (base)(height)/2
We're told that base (BC) has length 6
So, if BC = 6, what do you ESTIMATE for the height of the triangle?
I'd say the height is 4 or 5.
Let's try something in the middle. Let's say the height = 4.5
Using these values, we get: area ≈ (6)(4.5)/2
≈ 27/2
≈ 13.5
Now let's check our answer choices to see which one is closest to 13.5
ASIDE: By test day, all students should have the following approximations memorized:
√2 ≈ 1.4
√3 ≈ 1.7
√5 ≈ 2.2
A) 9√3 ≈ 9(1.7) ≈ 15 (pretty close!)
B) 18√3 ≈ 18(1.7) ≈ 30 (not close)
We can stop here since the remaining answer choices will be greater than 30
Since A is the ONLY answer choice that's even close to our estimate of 13.5, we can be quite certain that the correct answer is A
RELATED VIDEO FROM OUR COURSE (Assumptions and Estimation on the GMAT)
