Question
The ratio of the speed of boat in upstream to speed of
boat in downstream is 7:9. If the boat can cover a total of 70 km upstream and 90 km downstream in 5 hours, then find the time taken by the boat to cover 200 km in still water.Solution
Let speed of boat in upstream and downstream be ‘7x’ km/h and ‘9x’ km/h respectively. 70/7x + 90/9x = 5 10/x + 10/x = 5 20 = 5x x = 4 Speed of boat in still water = (7x + 9x)/2 = 8x = 8 × 4 = 32 km/h Desired time = 200/32 = 6.25 hours
The value of i ∙ (j × k) + j∙ (i× k)+ k∙ (i × j) =Â
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