GRE math question r(t)=d question?
November 2nd, 2010 | 
Author:
Looking for info on gre preparation classes, gre preparation courses,gre test course and more?
Hi and welcome to my blog,
I opened this blog to help anyone who is preparing for his GRE exam.
I remember myself when I started - I was so lost and in such a panic.
Luckily I got this great Gre guide that helped me a lot
So study hard and good luck!
Two cars started from the same point and traveled on a straight course in opposite directions for exactly 2 hours, at which time they were 208 miles apart. If one car traveled, on average, 8 miles per hour faster than the other car, what was the average speed for each car for the 2 hour trip?
answer is 48 and 56.. please help ! how did they get this answer? i know i need two equations
Posted in 
Tags:
You’re right. Two equations, one for each car.
d1 = r1 * t1
d2 = r2 * t2
We know that t1 = 2hrs and t2 = 2 hrs, for starters.
We know that d1 + d2 =208.
And we know that (say) r1 = 8 + r2.
That looks like six equations in six unknowns, but only because I spelled it all out.
Substitute into d1 +d2 =208 and you’ll soon have one equation in one unknown, say r2.
Good luck!
If the slower car has av speed x then the faster car has av speed x+8
2[x+(x+8)]=208 which means 2x+8 = 104 or x = 48 which is the answer. What is "miles" by the way?
You know the total distance traveled is 208 miles over 2 hours.
One car’s speed was X and the other car’s speed was (X+8).
You know that distance = (rate)(time), so total distance = 2X + 2(X+8) = 208
Reduce this to: 4X + 16 = 208, X = 48 and X+8 = 56
Good luck on the GRE!
Princeton Review has a great program
2v+2(v+8)=208,4v=192 ,v=48 km/hr for slower car & 48+8=56 km/hr for faster car.
God bless you.
let average speed of slowest car = x mls/hr
mls / hr
miles in 2 hours so total distance travelled by both cars
miles and this is equal to 208 miles
= 208
then average speed of other car = ( x +
now distance = time X speed so first car travels 2x miles in 2 hours
and second car travels 2( x +
is 2x + 2( x +
ie 2x + 2( x +
2x + 2x + 16 = 208
4x = 208 – 16
4x = 192
x = 192 / 4
x = 48 mls / hr
average speed of second car is 48 + 8 = 56 mls / hr
hope this helps