A man can go on a motorboat with a speed of 18 km/hour in still water to a certain upstream point and return to the starting point in a river that flows at a speed of 14 km/hour. Find the average speed of the motorboat for the total journey.
Let the speed of the boat be b km/hour and the speed of the current be s km/hour. Average speed = 2xy/ (x+ y) (here, x is the speed of downstream and y is the speed of upstream) = (2 (b +s) (b-s))/ ((b+ s +b -s)) = (b2 – s2)/b = (324 - 196)/18 = 128/18 = 64/9 Km/h
6 16 ? 244 1,245 7,506 52,591
...54 58 85 ? 226 262
...1, 27, ?, 343, 729, 1331
Study the given pattern carefully and select the number that can replace the question mark (?) in it.
4 7 6
15 ? 21
44 68 60
If 6 4 x 5.75 9,
Then, (x²-1) = ?
...3456 1728 2592 6485 22680 102060
...Select the number from among the given options that can replace the question mark (?) in the following series.
64, 60, 52, 40, ?, 4
19 20 29 54 103 ?
100 180 294 448 648 ?
398 308 228 158 98 ?
