The speed of a subway train is represented by the equation z=s^2+2s for all situations where 0 ≤ s ≤ 7, where z is the rate of speed in kilometers per hour and s is the time in seconds from the moment the train starts moving. In kilometers per hour, how much faster is the subway train moving after 7 seconds than it was moving after 3 seconds?
A. 4
B. 9
C. 15
D. 48
E. 63
The OA is D.
I don't have clear this PS question.
I just need to evaluate the speed equation for z(7) and z(3) and then find the difference between them? I appreciate if any expert explains it to me. Thank you so much.
The speed of a subway train is represented by the equation..
This topic has expert replies
- DavidG@VeritasPrep
- Legendary Member
- Posts: 2663
- Joined: Wed Jan 14, 2015 8:25 am
- Location: Boston, MA
- Thanked: 1153 times
- Followed by:128 members
- GMAT Score:770
You're exactly right.AAPL wrote:The speed of a subway train is represented by the equation z=s^2+2s for all situations where 0 ≤ s ≤ 7, where z is the rate of speed in kilometers per hour and s is the time in seconds from the moment the train starts moving. In kilometers per hour, how much faster is the subway train moving after 7 seconds than it was moving after 3 seconds?
A. 4
B. 9
C. 15
D. 48
E. 63
The OA is D.
I don't have clear this PS question.
I just need to evaluate the speed equation for z(7) and z(3) and then find the difference between them? I appreciate if any expert explains it to me. Thank you so much.
Her speed at 7 seconds: 7^2 + 2*7 = 49 + 14 = . 63
Her speed at 3 seconds: 3^2 + 2*3 = 9 + 6 = 15
The difference 63-16 = 48. The answer is D
GMAT/MBA Expert
- Scott@TargetTestPrep
- GMAT Instructor
- Posts: 7243
- Joined: Sat Apr 25, 2015 10:56 am
- Location: Los Angeles, CA
- Thanked: 43 times
- Followed by:29 members
z(7) = 7^2 + 2(7) = 49 + 14 = 63AAPL wrote:The speed of a subway train is represented by the equation z=s^2+2s for all situations where 0 ≤ s ≤ 7, where z is the rate of speed in kilometers per hour and s is the time in seconds from the moment the train starts moving. In kilometers per hour, how much faster is the subway train moving after 7 seconds than it was moving after 3 seconds?
A. 4
B. 9
C. 15
D. 48
E. 63
.
z(3) = 3^2 + 2(3) = 9 + 6 = 15
So the difference is 63 - 15 = 48.
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