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

Redeem

Product of ab

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Legendary Member
Posts: 510
Joined: Thu Aug 07, 2014 2:24 am
Thanked: 3 times
Followed by:5 members

Product of ab

by j_shreyans » Tue May 19, 2015 8:58 am
If a and b are two integers such that a is even, b is odd and neither of them leaves a remainder of 1 when divided by 10, what is the units digit of the product ab?

1) The units digit of a^3 is the same as the units digit of a.
2) The units digit of b^4 is the same as the units digit of b.

OAB
Top
Source: — Data Sufficiency |
Master | Next Rank: 500 Posts
Posts: 111
Joined: Sat Mar 07, 2015 11:00 pm
Thanked: 8 times
Followed by:1 members

by binit » Wed May 20, 2015 1:21 am
My take:

a is even. b is odd. a or b not equals 1, 11, 21, 31 etc.

St 1: Units digit of a^3 = Units digit of a.
So, a can be 4, 5, 6 or 9. But a is even. So, a = 4 or 6.
But we have no idea about b, hence we can't say anything about units digit of ab. INSUFFICIENT.

St 2: Units digit of b^4 = Units digit of b.
So, b can be 1, 5 or 6. b is odd so 6 is out. b can't be 1, as the problem states. So, b = 5.
If b is 5 and a is even, the units digit of ab has to be ZERO. SUFFICIENT.
Note: This is very mistake prone to choose C after doing all this, I did :wink: but finally realized.

~Binit.
- - - - -
A thanks will be appreciated if u like my post. :)
Top
Post new topic Post Reply
• Page 1 of 1