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Official Guide - 2nd Edition

by shanice » Thu May 17, 2012 11:21 pm
Hi all,

Please help me with the below question:-

At a monthly meeting, 2/5 of the attendees were males and 7/8 of the male attendees arrived on time. If 9/10 of the female attendees arrived on time, what fraction of the attendees at the monthly meeting did not arrive on time?

(A)11/100
(B)3/25
(c)7/50
(d)3/20
(e)4/25

Answer is A.

My workings:-

2/5 x Attendees = 2/5A were males so 3/5A should be females.
7/8 x 2/5A = 7/20A - arrived on time so 13/20A did not arrive on time.

Whereas, for the females, 3/5A x 9/10 = 27/50A arrived on time so 23/50A did not arrive on time.

Since the question wants us to find the fraction of the attendees at the monthly meeting that did not arrive on time, so it should be 13/20A + 23/50A = 111/100.

However, my answer is wrong. Can anybody help me, please?

Thank you in advance.
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by mdavidm_531 » Fri May 18, 2012 2:16 am
shanice wrote:Hi all,

Please help me with the below question:-

At a monthly meeting, 2/5 of the attendees were males and 7/8 of the male attendees arrived on time. If 9/10 of the female attendees arrived on time, what fraction of the attendees at the monthly meeting did not arrive on time?

(A)11/100
(B)3/25
(c)7/50
(d)3/20
(e)4/25

Answer is A.

My workings:-

2/5 x Attendees = 2/5A were males so 3/5A should be females.
7/8 x 2/5A = 7/20A - arrived on time so 13/20A did not arrive on time.

Whereas, for the females, 3/5A x 9/10 = 27/50A arrived on time so 23/50A did not arrive on time.

Since the question wants us to find the fraction of the attendees at the monthly meeting that did not arrive on time, so it should be 13/20A + 23/50A = 111/100.

However, my answer is wrong. Can anybody help me, please?

Thank you in advance.
Hello, Shanice,

When faced with overlapping sets, it would be best to use a double matrix.

I think you used it and kudos to you.

However, the next challenge is to read the question carefully. This separates the 700+ students to the rest of the pack. They (700+ students) are very critical in filling up the double matrix table. Remember that the GMAT is like a minefield. It is full of traps.

That being said, here is my double matrix.



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by kullayappayenugula » Fri May 18, 2012 3:41 am
hi,


Assume the number of attendess to be 100.

Now 2/5 of the attendees are male => 40
the rest are femlae => 60

Now 7/8 of the male attendees have arrived on time => 40*(7/8) = 35

=> the number of male who came late are 40 - 35 = 5

Similarly we calculate for women.

The number of female on time = 60*(9/10) = 54 => 6 have come late. (60 - 54)

So the total no. of attendees who are late is 11 out of 100 => the answer is 11/100
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by Anurag@Gurome » Fri May 18, 2012 3:47 am
Algebraic Method:

Let us assume that the total number of attendees = N
Number of males = 2N/5
Number of females = N - 2N/5 = 3N/5
Males who did not arrived on time = 2N/5 - 7(2N/5)/8 = 2N/5 * (1 - 7/8) = N/20
Females who did not arrived on time = 3N/5 * (1 - 9/10) = 3N/50
Total number of late arrivals = N/20 + 3N/50 = 11N/100

Therefore, required fraction = 11N/100/N = [spoiler]11/100[/spoiler]

The correct answer is A.
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by shanice » Fri May 18, 2012 5:35 am
Thank you, guys.
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