Here we go, since the question is Data Sufficiency we do not need exact answer, just get the gist.

You know that Time = Distance/Speed, and from here we can find either value, yep?

Let the Speed be X, Distance D and Time Spent D/X - all the usual indicators

However, Today occurred some changes as follow:

TODAY: - Speed Today X/1.5 (1.5 times slower) and Time Spent 1.5D/X and the Distance remain the same, lets now move to options what we got:

1. From Statement 1 we get that 1.5D/X - D/X = 15/60 --->>>> a little bit manipulation gives us that D/X = 1/2, OR usual time (Before) it took Bill 1/2 hour or 30 minutes to drive to school, hence Sufficient.

2. The distance between home and school is irrelevant here, it can not help us that much, thus Insufficient.

Therefore, answer would be (A)

Please, correct me if I went awry.

dczuchta wrote:

Driving 1.5 times slower, Bill was late for school today. What is the usual time it takes Bill to drive to school? (Assume that each day Bill takes the same route).

1) It took Bill 15 more minutes to drive to school today than usually

2) The distance between home and school is 15 miles

Source: GMAT Club Tests - hardest GMAT questions

S1 tells us that on average Bill drives for 15 minutes less. Since he drove 1.5 times slower, the 15 minutes account for the difference. Therefore, it is possible to find the difference.

(Can Someone Please Explain to Me Here In an Equation HOw we Can come up with that Answer if We Needed To. Thank you.S2 does not tell us much; we don't really need to know the distance and by itself it is insufficeint.

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God loves the steadfast.