guys here are some good DS problems ... try and solve them ..

q.) Train A leaves New York for Boston at 3 PM and travels at the constant speed of 100 mph. An hour later, it passes Train B, which is making the trip from Boston to New York at a constant speed. If Train B left Boston at 3:50 PM and if the combined travel time of the two trains is 2 hours, what time did Train B arrive in New York?
(1) Train B arrived in New York before Train A arrived in Boston.

(2) The distance between New York and Boston is greater than 140 miles.

q.)Last Friday a certain shop sold 3/4 of the sweaters in its inventory. Each sweater sold or $20. What was the total revenue last Friday from the sale of these sweaters?

(1) When the shop opened last Friday, there were 160 sweaters in its inventory.
(2) All but 40 sweaters in the shop's inventory were sold last Friday.

q.) 8x(y^3) + 8 (x^3)y = [2(x^2)(y^2)] / [2^(-3)]

What is xy?

(1) y>x
(2) x<0

Hi

I am unable to understand the second equation you had derived in the first problem.

"and 100 + B/6 = x (for train B to reach NY, it has to travel x distance)"

Request you to help.

Prasanna

Gabriel, I had a good mental workout . I seriously hope such
questions won't show up on GMAT or show up as experimental
questions.

I think it should be D.

The question stem can be translated into equations of the form below --

x = distance between NY and BOS
B = speed of train B

We know x/100 + x/B = 2
and 100 + B/6 = x (for train B to reach NY, it has to travel x distance)

Using 2 in 1, we get

B^2 - 500B + 60000 = 0
B = 200 or 300
Correspondingly x = 150 or 800/6

1 tells us that B arrived before A. Only B=300 satisfies this.
If we choose B=200, A will arrive at 4:20 and B will arrive at 4:30
If we choose B=300, A will arrive at 4:30 and B will arrive at 4:20


2 tells us that x > 140 which implies it has to be 150 and hence
sufficient.


1 - sufficient. 3/4 * 160 * 20 is the revenue
2 - sufficient. 1/4 of inv = 40, so 3/4 = 120. So revenue = 120 * 20

Hence D


We can translate the equation to

8xy (x^2 + y^2) = 8xy(2xy)
8xy*(x-y)^2 = 0

So, xy = 0 or (x-y)^2 = 0

1 - sufficient. x-y cannot be zero. So xy = 0

2 - insufficient. If x = y, then xy need not be zero. If x != y, then xy = 0

So, I think it should be A