Four people need to cross a bridge that can only hold two people at a time . It ’ s dark , so they need a flashlight , but they only have one . Person A can cross in 1 minute , B in 2 minutes , C in 5 minutes , and D in 10 minutes . When two people cross together , they must move at the slower person ’ s pace . How can they all get across in 17 minutes ?
CRANIUM CHALLENGE
How Can they all Cross a Bridge at Night in 17 Minutes ?
Four people need to cross a bridge that can only hold two people at a time . It ’ s dark , so they need a flashlight , but they only have one . Person A can cross in 1 minute , B in 2 minutes , C in 5 minutes , and D in 10 minutes . When two people cross together , they must move at the slower person ’ s pace . How can they all get across in 17 minutes ?
Please send your answers to Thomas Selling via e-mail : thomasselling @ me . com Correct responses will be recognized in the future issues of the New Hampshire Civil Engineer
Let the first four digits be a , b , c , and d . According to the question , a = d / 4 , b = 6a , and c = b + 3 Convert each equation in terms of d . Now , use the hit and trial method to find the value of d from 0 to 9 . If we take values 0 to 3 for d , a would be either 0 or a fraction . So , let ’ s take d = 4 , then a = 1 , b = 6 , and c = 9 All these satisfy the conditions given . Therefore , the four-digit number will be 1694 .
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