Nidzo
As train X leaves \(1.5\) hours before train Y and travels at \(x\) mph, then train X will be \(1.5x\) miles ahead when Y begins its trip.
As Y is travelling at a faster speed of \(y\) mph, their relative speed will be \(y - x\).
This means that \(y\) will pass \(x\) after (formula for time = distance/speed): \(\frac{1.5x}{y-x}\)
(1) y = 4x/3Plugging this into \(\frac{1.5x}{y-x}\) gives:
\(\frac{1.5x}{\frac{4}{3}x-x}\)
\(\frac{1.5x}{\frac{1}{3}x}\)
\(4.5\) hours.
SUFFICIENT(2) x = 60 miles per hourPlugging this into \(\frac{1.5x}{y-x}\) gives:
\(\frac{90}{y-60}\)
As we know nothing about \(y\) we cannot solve the question with only this info.
INSUFFICIENTANSWER A Nice approach....I will solve it this way:
Background: Since X left before Y, total time that X will spend at the point when they both catch up will be greater by 1.5hrs
So we can let time spent by Y at point of catch up be T, the. X will spend (T+1.5)hr.
At the catch up point, both parties must have travelled the same distance. We can put this in math form;
xT=y(T+1.5).....eq1
statement
1. 4x/3=y
Eq 1 above can be written as
xT=4x/3(T+1.5)
*Since x cannot be zero ( this can be infer from free info)*- This is a simple but powerful mindset that I think we should always keep i mind when working with equation like this.
We can cancel out x in both side.
Thus, T can be solved for. Stm 1 is sufficient
2.
x=60
inserting this into eq 1 above, we have:
60T=y(T+1.5)
We have 2 unknown, hence T can not be solved for...Not sufficient
P.S D=S×T
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