• # question_answer Places M and N are 90 km apart from each other on a national highway. A truck starts from M and another from N at the same time. If they go in the same direction, then they meet in 9 hours and if they go in opposite directions they meet in - hours. The speed of the trucks are ____.   A)  90 km/hr, 40 km/hr               B)  40 km/hr, 30 km/hr                C)  20 km/hr, 60 km/hr              D)  50 km/hr, 12 km/hr

Let x km/hr be the speed of truck starting from M and y km/hr be the speed of truck starting from N.                                       Case I: If they meet at P. Speed $=\frac{Distance}{Time}$ For M, $x=\frac{90+a}{9}$ or$9x=90+a$             For N, $y=\frac{a}{9}$  or  $9y=a$                      $\Rightarrow$   $10+y=x$                        ...(1) Case II: If they meet at P. For M, $x=\frac{a}{9/7}$ and For N, $y=\frac{9-a}{9/7}$ $\Rightarrow$  $70=x+y$                        ...(2) Solving (1) and (2), we get $y=30\text{ }km/hr$and $x=40\text{ }km/hr$
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