help needed on word problem

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

Redeem

This topic has expert replies

Post new topic Post Reply

Previous Topic Next Topic

sohaib_iba: Junior | Next Rank: 30 Posts; Posts: 12; Joined: Wed Feb 24, 2010 7:09 am

help needed on word problem

by sohaib_iba » Wed Feb 24, 2010 7:16 am

Ellen paid $11.80 for 40 postage stamps. If some of the stamps were 33-cent stamps and the rest were 23-cent stamps, how many 33-cent stamps did she buy?

A) 13
B) 17
C) 22
D) 25
E) 26

Please help me at this question as i am unable to solve it yet. Thanks in advance

Quote

Source: Beat The GMAT — Problem Solving | Wed Feb 24, 2010 7:16 am

ldoolitt: Master | Next Rank: 500 Posts; Posts: 184; Joined: Sat Apr 14, 2007 9:23 am; Location: Madison, WI; Thanked: 17 times

by ldoolitt » Wed Feb 24, 2010 7:39 am

sohaib_iba wrote:Ellen paid $11.80 for 40 postage stamps. If some of the stamps were 33-cent stamps and the rest were 23-cent stamps, how many 33-cent stamps did she buy?

A) 13
B) 17
C) 22
D) 25
E) 26

Please help me at this question as i am unable to solve it yet. Thanks in advance

I get 26.

The question stem screams EQUATIONS. And this stem gives you two. First set up your variables

X = quantity of 33 cent postage stamps (your answer)
Y = quantity of 23 cent postage stamps

(1) X+Y = 40 (since you have 40 total stamps)
(2) .33*X + .23*Y = 11.80 (since you paid 11.80 for all the stamps)

Take (2) and multiply through by 100 to clear out the decimals

33*X + 23*Y = 1180

Take (1) and multiply through by -23

-23*X - 23*Y = 40*-23

Add these two together. Skipping the arithmetic involved in canceling the Y's:

10*X = 1180 - 40*23
X = 118 - 4*23
X = 26