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If a, b, c, and d are positive integers, what is the value.. [#permalink]
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Updated on: 22 Dec 2012, 08:31
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70% (00:58) correct 30% (01:07) wrong based on 299 sessions
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If a, b, c, and d are positive integers, what is the value of (a + b)(c + d)? (1) 4a! = b! (2) 5c! = d!
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Originally posted by daviesj on 22 Dec 2012, 07:46.
Last edited by daviesj on 22 Dec 2012, 08:31, edited 1 time in total.



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Re: If a, b, c, and d are positive integers, what is the value.. [#permalink]
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22 Dec 2012, 08:06
I just stumbled onto the "!" symbol in math, so I cannot solve this problem. However I've got a question! (Let's say a = 2) When it was 4a!, does that equal 4*1*2, or does it equal 1*2*1*2*1*2*1*2? I'm a bit confused as of which order to do things.



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Re: If a, b, c, and d are positive integers, what is the value.. [#permalink]
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22 Dec 2012, 08:22
If a, b, c, and d are positive integers, what is the value of (a + b)(c + d)? (1) 4a! = b! (2) 5c! = d! Hi, Statement 1: 4a! = b! so (a,b) have only one valid case (3,4) so values are a=3 and b=4 Statement 1: 5c! = d! so (c,d) have only one valid case (4,5) so values are c=4 and b=5 Ans: (3+4)(4+5) => 7*9 C
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Status: Never ever give up on yourself.Period.
Joined: 23 Aug 2012
Posts: 148
Location: India
Concentration: Finance, Human Resources
GMAT 1: 570 Q47 V21 GMAT 2: 690 Q50 V33
GPA: 3.5
WE: Information Technology (Investment Banking)

Re: If a, b, c, and d are positive integers, what is the value.. [#permalink]
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22 Dec 2012, 08:25
700+ questions are never much difficult,they are just tricky... In this problem if you can see carefully, only one combination of a and b satisfies 4a! = b!...well, how's that? simple for a=3... a! will be 3*2*1 and 4*a! will be 4*3*2*1 i.e. 4! so b=4...no other value of a would satisfy this.. Same is the case with 5c! = d! .i.e c=4 and d=5. Sentence 1: not sufficient as it gives only the values of a & b Sentence 2: not sufficient as it gives only the values of c & d both sentences together: can solve the problem as we get all the values hence the answer 'C' Hope the point is clear.. :)
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Re: If a, b, c, and d are positive integers, what is the value.. [#permalink]
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23 Dec 2012, 04:28
If a, b, c, and d are positive integers, what is the value of (a + b)(c + d)? (1) 4a! = b! (2) 5c! = d! all u need to know are values of positive integers a,b,c &d. statement1:talks about only a and b .no info reg c&d .insuff statement2:talks about only c&d.no info reg a&b.insuffi. combining 1 &2 only values which will work for a&b are a=3,b=4,c&d are c=4,d=5.sufficient. C is the answer



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Re: If a,b,c,and d are positive integers,what is the value of [#permalink]
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02 Mar 2013, 19:27
We are given that a,b,c, and d are positive integers and need to find the value of (a+b) (c+d) Consider statement (1) first 4a! = b! This can only be true if a=3 and b=4. However this does not give us the value of c and d and is insufficient. Consider statement (2) next 5c! = d! This can only be true if d=5 and c=4. However this does not give us the value and a and b and is insufficient. Combining both, we have the values of a,b,c, and d. Sufficient. C is the answer.
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Re: If a, b, c, and d are positive integers, what is the value.. [#permalink]
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29 Nov 2016, 05:22
4a!=b! means (b!/a!)=4, the only possibility is 4!/3!
5c!=d! means (d!/c!)=5, the only possibility is 5!/4!
C



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Re: If a, b, c, and d are positive integers, what is the value.. [#permalink]
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