I did get A for this answer.

You know the second (bottom) route will DEFINITELY exit at Y. So there is 1/2 already or 50%. So you need to determine how many chances you have from the first route.

So let's just follow the map here. Remember, we're starting from 50%.

First split - 50/50 again or 50/50 of (50%) which comes out 25%/25%. You know the bottom route follows the error to Y. So you have another 25% chance.

So far, you have 50% + 25%.

now the top split, (which was 25% left over) it splits again; one going to X and another going down to Y. So that's another 50/50 of 25%, which equals 12.5% each.

So now you have 50% + 25% + 12.5% = 87.5%.

This is measuring your capabilities of how to use the fraction of fractions.

I wish I can draw on the picture to explain it better.

where are you getting these questions from?

Thanks,

this looks complicated but is quite simple.
let total traffic be X
now we can clearly see X/2 goes to Y from C which is later joined by X/4 and X/8.
this gives us total=x/2+x/4+x/8=7x/8
percent through y=(7*100)/8=87.5% answer is A

hwiya320 wrote:where are you getting these questions from?

Thanks,

These are retired GMAT questions from the sets.