Four people on a rickety bridge

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When I turned BBC news on this morning, the first words I heard were ’emotional well-being’ and ‘cognitive decline’. Research has shown that a dexterous brain makes for happier, healthier people in general. Brain teasers and logic puzzles are one way to boost our mental fitness.

My first riddle blog is inspired by the classic ‘bridge crossing’ problem and its one of the famous Microsoft interview puzzles used to test the problem-solving skills of prospective employees. Don’t be deceived by what seems to be the evident way, it is a bit more tricky and when you think logically, you will understand why.

The last hurdle on the way home for the family of four – father, mother, son and daughter – is the rickety bridge. It is getting dark and between the four, they have only one torch and the bridge cannot be crossed without the use of the torch. The bridge is way too long for the torch to be thrown from one side to the other, and the bridge can only carry two people at a time. Each person can traverse the bridge in a different time. Ben, the son, is the fastest and can cross the bridge in 1 minute. His father in two minutes, his sister, Leah, in five minutes and his mum, who needs a bit longer to get her way across, in 10 minutes. What is the shortest time needed for all four of them to cross the bridge?

Try not to cheat by searching for the solution on the internet. The solution will be revealed in a next blog post.

References:

Bellos, A. (2016) Can you solve my problems?, London Guardian Books and Faber and Faber Ltd,, available at https://amzn.to/2t8le3L/

Elements in the illustration: bridge in nature, family and torch by Vecteezy. Accessible at https://www.vecteezy.com/

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