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Tutor Joined: 20 Apr 2012
Posts: 97
Location: Ukraine
GMAT 1: 690 Q51 V31 GMAT 2: 730 Q51 V38 WE: Education (Education)
In triangle JKL shown above, B divides side KL in such a way  [#permalink]

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9 00:00

Difficulty:   95% (hard)

Question Stats: 47% (02:16) correct 53% (02:39) wrong based on 94 sessions

HideShow timer Statistics In triangle JKL shown above, B divides side KL in such a way that KB : BL = 1 : 3 and C divides side JL in such a way that JC : CL = 1:2. What is the area of triangle BCL?

(1) The area of triangle JKL is 96

(2) The length of side KL is 24

It is very easy to solve this problem if you know the formula of triangle's area with sine. Any suggestions how to solve it quickly without trigonometry?

Source: GoGMAT

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Joined: 02 Sep 2009
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Re: In triangle JKL shown above, B divides side KL in such a way  [#permalink]

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4 In triangle JKL shown above, B divides side KL in such a way that KB : BL = 1 : 3 and C divides side JL in such a way that JC : CL = 1:2. What is the area of triangle BCL?

(1) The area of triangle JKL is 96.

Notice that since KB:BL=1:3, then BL=3/4*KL and since JC:CL=1:2, then CL=2/3*JL.

$$area_{JKL}=\frac{1}{2}*(height)*KL=96$$.
$$area_{JBL}=\frac{1}{2}*(height)*BL=\frac{1}{2}*(height)*(\frac{3}{4}*KL)=\frac{3}{4}*(\frac{1}{2}*(height)*KL)=\frac{3}{4}*area_{JKL}=72$$.

Similarly, $$area_{BCL}=\frac{2}{3}*area_{JBL}=48$$. Sufficient.

(2) The length of side KL is 24. Clearly insufficient.

Hope it's clear.
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Tutor Joined: 20 Apr 2012
Posts: 97
Location: Ukraine
GMAT 1: 690 Q51 V31 GMAT 2: 730 Q51 V38 WE: Education (Education)
Re: In triangle JKL shown above, B divides side KL in such a way  [#permalink]

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Very clear! Thanks!

Anyway with trigonometry the solution is much faster:)
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Re: In triangle JKL shown above, B divides side KL in such a way  [#permalink]

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Bunuel wrote: In triangle JKL shown above, B divides side KL in such a way that KB : BL = 1 : 3 and C divides side JL in such a way that JC : CL = 1:2. What is the area of triangle BCL?

(1) The area of triangle JKL is 96.

Notice that since KB:BL=1:3, then BL=3/4*KL and since JC:CL=1:2, then CL=2/3*JL.

$$area_{JKL}=\frac{1}{2}*(height)*KL=96$$.
$$area_{JBL}=\frac{1}{2}*(height)*BL=\frac{1}{2}*(height)*(\frac{3}{4}*KL)=\frac{3}{4}*(\frac{1}{2}*(height)*KL)=\frac{3}{4}*area_{JKL}=72$$.

Similarly, $$area_{BCL}=\frac{2}{3}*area_{JBL}=48$$. Sufficient.

(2) The length of side KL is 24. Clearly insufficient.

Hope it's clear.

Hi,

I have a different method.

Let angle L = Ø
As we know area of triangle = (1/2) * Product of two sides * sin(included angle)
Let KB = x, BL = 3x, KL = 4x
Let JC = y, CL = 2y, JL = 3y

St1: The area of triangle JKL is 96.

area(JKL) = (1/2)* KL * JC * sinØ =
(1/2)*4x*3y*sinØ = 96 --- {1}
area(BCL) = (1/2)*BL*CL*sinØ =
(1/2)*3x*2y*sinØ = area(BCL) ---{2}

dividing eqn {1} by {2}, we get area(BCL) = 48

Sufficient!

ST2: length of side KL = 24. We need three factors to define a triangle (two sides and one angle).

Insufficient!

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Re: In triangle JKL shown above, B divides side KL in such a way  [#permalink]

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_________________ Re: In triangle JKL shown above, B divides side KL in such a way   [#permalink] 15 Feb 2019, 03:36
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