BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

different positive integers a,b,c are divisible by 7

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 748
Joined: Sun Jan 31, 2010 7:54 am
Thanked: 46 times
Followed by:3 members

different positive integers a,b,c are divisible by 7

by outreach » Sat Mar 13, 2010 1:38 pm
How many of the three different positive integers a,b,c are divisible by 7
1. product of a,b,c is divisible by 3 but only c is divisible by 21
2. each of the positive integers is divisible by 3 but only c is divisible by 21


OAB
-------------------------------------
--------------------------------------
General blog
https://amarnaik.wordpress.com
MBA blog
https://amarrnaik.blocked/
Top
Source: — Data Sufficiency |
Legendary Member
Posts: 610
Joined: Fri Jan 15, 2010 12:33 am
Thanked: 47 times
Followed by:2 members

by kstv » Sat Mar 13, 2010 10:20 pm
1. product of a b c is divisible by 3 and c is divisible by 21 so c can be expressed as 21x where x is any integer.
a*b*c = ab(7*3 x ) this is divisible by 3 without any restriction to the values a and b can take. Insuff.

2. a= 3y b = 3z c = 21z x, y and z are any integers
here a and b can be any multiple of 3 except 7 as only c is divisible by 21
i.e y can be 1 2 3 4 5 6 _ 8 9 (8 values) and z (7 values as it cannot be same as y)

Is that Suff ?

My answer was E but OA is B
Top
Master | Next Rank: 500 Posts
Posts: 114
Joined: Mon Sep 22, 2008 3:51 am
Thanked: 8 times
GMAT Score:680

by Fiver » Sun Mar 14, 2010 12:19 am
Choose B.

St1] product of a,b,c is divisible by 3 but only c is divisible by 21
E.g a=1 , b=3,c=21 :Only c is divisible by 7.
a=7, b=7, c=21 : All are divisible by 7.
a=1, b=7, c=21 : b& c are divisible by 7.

St2] each of the positive integers is divisible by 3 but only c is divisible by 21
Since 21 = 7*3, any integer multiple of 3 & 7 must be divisible by 21 also.
Hence according to st2] a & b have 3 as a factor but not 7.
So only c is divisible by 7.
Top
Post new topic Post Reply
• Page 1 of 1