AboutRohit Agarwal Expertise I can answer questions related to numbers and logic easily. However I sometimes face problems when solving questions that require a lot of creative thinking. I am not good at puzzles which involve a play with words, so please don't ask me to solve such puzzles for you.
Experience I have read a couple of good books containing puzzles and can now claim to have an "expert" in this field. I have been invited to become a member of Mensa.
Organizations INDIAN INSTITUTE OF TECHNOLOGY, DELHI
Education/Credentials Currently doing Dual Degree (B.Tech M.Tech) in Electrical Engineering Department from INDIAN INSTITUTE OF TECHNOLOGY, DELHI
Awards and Honors Numerous certificates recognizing my ability in Mathematics and Logical Thinking
Question calum was floating down on a raft,when half a mile downstream,his brother duncan set off in a canoe. duncan paddled downstream as quickly as he could, then turned round and paddled back again, still at his best pace. he arrived back at his starting point just as calum floated by. assuming duncans best pace in still water is 10 times that of the river current, how far did he paddle.
explain your answer.
Answer Let's assume that the velocity of the stream in the river is 'v' miles per hour. Then, the velocity of Duncan is 10v. Hence his downstream velocity is 10v + v (=11v) and his upstream/return velocity is 10v-v (=9v). Also let's assume that he paddles as far as 'd' miles.
Now,
Time taken for Duncan to go downstream = d/11v
Time taken for Duncan to go upstream (i.e. return to his starting point) = d/9v
Time taken for Calum to reach Duncan's starting point = 0.5/v
According to the problem statement, we have
d/11v + d/9v = 0.5/v
i.e. d*(1/11 + 1/9) = 1/2
On solving, obtain the value of d as 2.475 miles.
Hope it helps.
PS1: Next time onwards, please include a "please" in your question
PS2: This is a standard classroom problem for children aged 14-15 years in the country I live in.
