trip on an expressway

Feruza Matyakubova wrote:please, help to solve this one in 90 seconds...

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!

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 %

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)

logitech wrote:

Feruza Matyakubova wrote:please, help to solve this one in 90 seconds...

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!

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?

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