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10 Jul 2025, 08:00
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E
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Difficulty:
35%
(medium)
Question Stats:
76% (01:21) correct
24%
(01:10)
wrong
based on 251
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Over a 4-hour shift, Mark loaded a total of 80 boxes into a truck. What was the average (arithmetic mean) weight of the boxes he loaded during the shift?
(1) During the first 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 20 kilograms.
(2) During the last 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 30 kilograms.
(1) During the first 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 20 kilograms.
(2) During the last 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 30 kilograms.
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10 Jul 2025, 08:30
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Over a 4-hour shift, Mark loaded a total of 80 boxes into a truck. What was the average (arithmetic mean) weight of the boxes he loaded during the shift?
This is not a hard problem per se, but if read carelessly, one can easily make a blunder.
(1) During the first 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 20 kilograms.
This statement is clearly insufficient because it provides no information about the second half of the shift.
(2) During the last 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 30 kilograms.
Similarly, this statement is insufficient since it provides no information about the first half of the shift.
(1) + (2) When taken together, note that we cannot assume Mark loaded half the boxes in each half of the shift. Since we don’t know how many boxes were loaded during each half, we cannot compute the overall average.
For example, if 1 box weighing 20 kg was loaded in the first half and 79 boxes averaging 30 kg in the second half, the overall average would be (1 * 20 + 79 * 30)/80 = 29.something. But if 79 boxes averaging 20 kg were loaded in the first half and 1 box weighing 30 kg in the second half, the overall average would be (79 * 20 + 1 * 30)/80 = 20.something kg. Not sufficient.
Answer: E.
GMAT Club Official Explanation:
Over a 4-hour shift, Mark loaded a total of 80 boxes into a truck. What was the average (arithmetic mean) weight of the boxes he loaded during the shift?
This is not a hard problem per se, but if read carelessly, one can easily make a blunder.
(1) During the first 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 20 kilograms.
This statement is clearly insufficient because it provides no information about the second half of the shift.
(2) During the last 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 30 kilograms.
Similarly, this statement is insufficient since it provides no information about the first half of the shift.
(1) + (2) When taken together, note that we cannot assume Mark loaded half the boxes in each half of the shift. Since we don’t know how many boxes were loaded during each half, we cannot compute the overall average.
For example, if 1 box weighing 20 kg was loaded in the first half and 79 boxes averaging 30 kg in the second half, the overall average would be (1 * 20 + 79 * 30)/80 = 29.something. But if 79 boxes averaging 20 kg were loaded in the first half and 1 box weighing 30 kg in the second half, the overall average would be (79 * 20 + 1 * 30)/80 = 20.something kg. Not sufficient.
Answer: E.
General Discussion
Emkicheru
Joined: 12 Sep 2023
Last visit: 12 Sep 2025
Posts: 119
Own Kudos:
Given Kudos: 11
Location: Kenya
Schools: Anderson (UCLA) Sloan (MIT) Columbia '27
GMAT 1: 780 Q50 V48
GRE 1: Q167 V164
GPA: 3.7
Schools: Anderson (UCLA) Sloan (MIT) Columbia '27
GMAT 1: 780 Q50 V48
GRE 1: Q167 V164
Posts: 119
Kudos:
22
10 Jul 2025, 08:28
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Bunuel
The average AM in the four hours is (20+30)=50/2=25
