How many multiples of 7 are between 21 and 343, exclusive?
A. 48
B. 47
C. 46
D. 45
E. 44
The OA is D.
Please, can any expert explain this PS question for me? I don't understand why that is the correct answer. Thanks.
How many multiples of 7 are between 21 and 343, exclusive?
This topic has expert replies
GMAT/MBA Expert
- Brent@GMATPrepNow
- 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
ASIDE: there are various formulas that students can memorize for this kind of question. Here's a solution that uses a nice easy rule (which can be applied in many ways):swerve wrote:How many multiples of 7 are between 21 and 343, exclusive?
A. 48
B. 47
C. 46
D. 45
E. 44
The number of integers from x to y inclusive equals y - x + 1
exclusive: so, we're not going to count 21 and 343
The multiples of 7 to be counted are:
28
35
42
.
.
.
336
We can REWRITE the values as follows:
28 = (7)(4)
35 = (7)(5)
42 = (7)(6)
.
.
.
336 = (7)(48)
So, we need only find the number of integers from 4 to 48 inclusive
Applying the above rule, the number of integers = 48 - 4 + 1 = 45
Answer: D
Cheers,
Brent
-
- GMAT Instructor
- Posts: 2630
- Joined: Wed Sep 12, 2012 3:32 pm
- Location: East Bay all the way
- Thanked: 625 times
- Followed by:119 members
- GMAT Score:780
21 = 7*3
343 = 7*49
So we want every multiple of 7 from 7*1 to 7*48, but we can't have 7*1, 7*2, or 7*3. That means we have 48 - 3 = 45 multiples.
343 = 7*49
So we want every multiple of 7 from 7*1 to 7*48, but we can't have 7*1, 7*2, or 7*3. That means we have 48 - 3 = 45 multiples.
GMAT/MBA Expert
- Scott@TargetTestPrep
- GMAT Instructor
- Posts: 7242
- Joined: Sat Apr 25, 2015 10:56 am
- Location: Los Angeles, CA
- Thanked: 43 times
- Followed by:29 members
We can calculate the number of multiples of 7, from 28 to 336 inclusive:swerve wrote:How many multiples of 7 are between 21 and 343, exclusive?
A. 48
B. 47
C. 46
D. 45
E. 44
The OA is D.
Please, can any expert explain this PS question for me? I don't understand why that is the correct answer. Thanks.
(336 - 28)/7 + 1 = 45
Answer: D
Scott Woodbury-Stewart
Founder and CEO
[email protected]
See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews