Problem 18 · 2017 Math Kangaroo
Stretch
Logic & Word Problems
work-backwardclock-calendar
Georg starts his training at 5 o'clock in the afternoon. It takes him 5 minutes to get to the bus stop. The bus journey takes 15 minutes. Then he has to walk for 5 minutes to get to the pitch. The bus comes for the first time and then every 10 minutes. What is the latest possible time he has to leave the house in order to be at the pitch on time?
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Answer: A
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Hint 1 of 2
Work backwards from 5 o'clock, peeling off the walk, the bus ride and the first walk.
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Hint 2 of 2
He must catch a bus, which only leaves every 10 minutes, so round to a bus time.
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Approach: work backward from 5:00 through each leg of the trip
- He must be at the pitch by 5:00; the last walk takes 5 min, so he leaves the bus by 4:55.
- The bus ride is 15 min, so he must board by 4:40 (a valid every-10-minutes time).
- The walk to the bus stop takes 5 min, so he must leave home by 4:35.
- The clock showing 4:35 is A.
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