Bunuel
A moving service charges p dollars for the first 5 miles of any trip plus 0.1*p dollars for each additional mile or fraction of a mile. If p > 30, was a particular trip more than 30 miles long?
(1) The moving service charged a total of 3.3p dollars for the trip.
(2) The moving service charged a total of $132 for the trip.
Experts' Global Explanation:Let total miles be M.
Cost for the first 5 miles =
p.
Cost for each of the remaining (M – 5) miles = 0.1
p.
Hence, the total cost for M miles =
p + 0.1
p(M – 5).
We need to find whether M > 30.
Statement (1)p + 0.1
p(M – 5) = 3.3
pCancelling all “
p”, we get: 1 + 0.1(M – 5) = 3.3
0.1(M – 5) = 2.3
M – 5 = 23
M = 28
It is possible to determine with certainty whether M is greater than 30; we can conclude that M is NOT greater than 30.
Hence, Statement (1) is sufficient.Trap alert! Many students may mistakenly believe that Statement (1) is insufficient, as “M = 28” leads to “No” as answer for “Is M > 30?”. Remember, in Data Sufficiency questions, a Statement is sufficient if it consistently leads to “No” as the answer.
Statement (2)p + 0.1
p(M – 5) = 132
p + 0.1
pM – 0.5
p = 132
0.5
p + 0.1
pM = 132
Multiplying both sides by 10, we get: 5
p +
pM = 1320
M = (1320/
p) – 5
Possibility 1: If
p = 100, then M < 30.
Possibility 2: If
p = 32, then M > 30.
It is NOT possible to determine with certainty whether M is greater than 30.
Hence, Statement (2) is insufficient.A is the correct answer choice.An interesting discussion:
A student once wrote to us asking whether Statement (1) would be sufficient if the calculated value for M turned out to be exactly 30.
Can you figure out the answer?
The given question asks us whether the value of M is strictly
greater than 30. Since the number 30 is
NOT greater than 30, we can determine with certainty that M is NOT greater than 30. Hence, Statement (1) would still be sufficient.