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

Redeem

Arithmetic

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Sun Nov 19, 2017 1:42 pm
Roland2rule wrote:If s and t are positive integers, st + s + t cannot be

A. 5
B. 6
C. 7
D. 8
E. 9
OA is b
Since the answer choices are small, and since s and t must be POSITIVE INTEGERS, a quick approach is to start testing pairs of values and using the results to eliminate answer choices.
Let's be somewhat systematic.
We'll try, s = 1 and t = 1, then s = 1 and t = 2, then s = 1 and t = 3, then s = 2 and t = 2, etc
Let's go.....

s = 1 and t = 1
st + s + t = (1)(1) + 1 + 1 = 3 (not there)

s = 1 and t = 2
st + s + t = (1)(2) + 1 + 2 = 5
ELIMINATE A

s = 1 and t = 3
st + s + t = (1)(3) + 1 + 3 = 7
ELIMINATE C

s = 1 and t = 4
st + s + t = (1)(4) + 1 + 4 = 9
ELIMINATE E

s = 2 and t =2
st + s + t = (2)(2) + 2 + 2 = 8
ELIMINATE D

By the process of elimination, the correct answer is B

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Post new topic Post Reply
• Page 1 of 1