FILE No.70Unsolved
A 260 lb safe was carried out of a vault using the building's only freight elevator. Its capacity is 770 lb, and exceeding it sounds an alarm. The night guard says the alarm never went off.
Two people rode with the safe and nobody else. The suspects weigh: Ann 190 lb, Ben 210 lb, Carl 290 lb, Dan 310 lb, Eve 330 lb.
Which pair could have ridden without setting off the alarm?
If you get stuck, open the hints one at a time, in order.
Subtract the safe from the capacity.
What is the most the two people can weigh together?
Add up each pair and compare.
Which pair could have ridden without setting off the alarm?
Choose the answer closest to the truth.
Ann and Ben (190 + 210 lb)
The answer is: Ann and Ben (190 + 210 lb).
The two people can weigh at most 770 - 260 = 510 lb in total. Carl and Eve: 620. Dan and Eve: 640. Ben and Eve: 540. All exceed 510. Ann and Ben: 400, under the limit. Only that pair is possible.
People see "770 lb" and forget to subtract the safe's 260 lb.
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