trip on an expressway
This topic has expert replies
- logitech
- Legendary Member
- Posts: 2134
- Joined: Mon Oct 20, 2008 11:26 pm
- Thanked: 237 times
- Followed by:25 members
- GMAT Score:730
I would either solve this with plugging numbers: But be careful and look at the answers before doing that since X=10 will make both %50 and 500/x options correct!Feruza Matyakubova wrote:please, help to solve this one in 90 seconds...
30=V
60=2V
so
Total time for (V..2V) = 5/v + (x-5)/2v = 5+x/2v
Total time for ( 2V ) = x/2V
So 5+x is what percent greater than x ?
(5+x-x)100/x = 500/X
Lets plug numbers:
X=15 miles
5 miles / 30 + 10 miles / 60 = 20/60 = lets say 20 minutes
15 miles / 60 = 15/60 = 15 minutes
20-15 = 5 minutes
So 5 minutes is what % of 15 minutes
5/15 = 0.33333333333333333333333
500/x = 500/15 = 33,3 %
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"
-
- Senior | Next Rank: 100 Posts
- Posts: 95
- Joined: Fri Sep 28, 2007 10:16 am
- Thanked: 6 times
- GMAT Score:710
Total time taken for the two segments of x-5 miles @ 60mph and 5 miles @ 30mph=
(x-5)/60 + 5/30 = (x-5+10)/60 = (x+5)/60
Time taken if all of x miles were traveled @ 60mph = x/60
Extra time take when 5 miles was done @ 30mph = (x+5)/60 - x/60
=5/60
Percentage increase= (increase/original)*100 = [(5/60)/(x/60)]*100= 500/x (E)
(x-5)/60 + 5/30 = (x-5+10)/60 = (x+5)/60
Time taken if all of x miles were traveled @ 60mph = x/60
Extra time take when 5 miles was done @ 30mph = (x+5)/60 - x/60
=5/60
Percentage increase= (increase/original)*100 = [(5/60)/(x/60)]*100= 500/x (E)
-
- Master | Next Rank: 500 Posts
- Posts: 154
- Joined: Tue Aug 26, 2008 12:59 pm
- Location: Canada
- Thanked: 4 times
logitech wrote:I would either solve this with plugging numbers: But be careful and look at the answers before doing that since X=10 will make both %50 and 500/x options correct!Feruza Matyakubova wrote:please, help to solve this one in 90 seconds...
30=V
60=2V
so
Total time for (V..2V) = 5/v + (x-5)/2v = 5+x/2v
Total time for ( 2V ) = x/2V
So 5+x is what percent greater than x ?
(5+x-x)100/x = 500/X
Lets plug numbers:
X=15 miles
5 miles / 30 + 10 miles / 60 = 20/60 = lets say 20 minutes
15 miles / 60 = 15/60 = 15 minutes
20-15 = 5 minutes
So 5 minutes is what % of 15 minutes
5/15 = 0.33333333333333333333333
500/x = 500/15 = 33,3 %
Yes I took X=15 and I got 20% not 33.3% like you did.
Did I do the calculations right?
-
- Master | Next Rank: 500 Posts
- Posts: 154
- Joined: Tue Aug 26, 2008 12:59 pm
- Location: Canada
- Thanked: 4 times
Ok got it working X = 15
d=vt so t=d/v
5/30 + 10/60 = 1/3
15/60 = 1/4
(1/3 - 1/4) / 1/4 = 1/3
* 100 for percentage 100/3
Choice that fits 500/15 = 100/3
d=vt so t=d/v
5/30 + 10/60 = 1/3
15/60 = 1/4
(1/3 - 1/4) / 1/4 = 1/3
* 100 for percentage 100/3
Choice that fits 500/15 = 100/3