Bunuel
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.
Over a 4 hour shift, Mark loaded a total of 80 boxes.
Average weight of boxes = ?
Average weight of boxes = ( Total weight) / ( Total number of boxes) = ( Total Weight) / 80
Statement 1:
(1) During the first 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 20 kilograms.
Let’s take the number of boxes that was loaded during first two hours as a.
Average Weight for first 2 hours = 20 = ( sum of weights loaded for first two hours)/ a
Sum of weights loaded for first two hours = 20*a
Hence, insufficient Statement 2:
(2) During the last 2 hours of the shift, the average (arithmetic mean) weight of the boxes Mark loaded was 30 kilograms.
Let the number of boxes loaded during the last two hours = b
Average Weight for Last 2 hours = 30 = ( sum of weights loaded for last two hours ) / b
Sum of weights loaded for last two hours = 30*b
Hence, insufficient Combining Statements 1 and Statements 2,
a + b = 80
Average weight = [ 20*a + 30* (80-a) ] / 80
= ( 20*a + 2400 - 30*a ) / 80
= ( 2400 - 10*a) /80
Hence, insufficient
Option E