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hard factorisation question

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Master | Next Rank: 500 Posts
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by jsl » Wed Oct 29, 2008 1:57 pm
If a and b are positive integers, is 3(a^2)b divisible by 60?

1) a is divisible by 10
2) b is divisible by 18

OA to follow shortly but I'll tell you that it isn't E!!
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Source: — Data Sufficiency |
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by stubbornp » Wed Oct 29, 2008 2:21 pm
stmt 1: a is divisible by 10

Min value for A is 10..

3(10)^2.b/60 = 300*b/60 = 5*b-----sufficient

Stmt 2:

b is divisible by 18

but we need atleast one factor of 5..---insufficient

A is answer
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Re: hard factorisation question

by logitech » Wed Oct 29, 2008 4:41 pm
jsl wrote:If a and b are positive integers, is 3(a^2)b divisible by 60?

1) a is divisible by 10
2) b is divisible by 18

OA to follow shortly but I'll tell you that it isn't E!!
if something is divisible by 60: you need to have 2x2x3x5 prime numbers in it

1) a is divisible by 10 means it has 2x5

the question can be simplified to is a^2b divisible by 20 ( 2x2x5)

so 1 is sufficient since a^2 will have 2x2x5x5 SUF

2) INSUF because 18 has no 5 as a prime factor

A
LGTCH
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