A mobike rider moving from A to B with speed 20km/h notices that a bus goes past it every 21 minute in the direction of his motion and every 7 minutes in the opposite direction.Velocity of the bus is a)25km/h b)35km/h c)30km/h d)40km/h


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Question Number 47810 by Necxx last updated on 15/Nov/18

$A m o b i k e r i d e r m o v i n g f r o m A t o B$ $w i t h s p e e d 20 k m / h n o t i c e s t h a t a$ $b u s g o e s p a s t i t e v e r y 21 m i n u t e i n$ $t h e d i r e c t i o n o f h i s m o t i o n a n d$ $e v e r y 7 m i n u t e s i n t h e o p p o s i t e$ $d i r e c t i o n . V e l o c i t y o f t h e b u s i s$ $a) 25 k m / h b) 35 k m / h c) 30 k m / h$ $d) 40 k m / h$
Commented by Necxx last updated on 15/Nov/18

$p l e a s e h e l p$
	Answered by mr W last updated on 15/Nov/18

	$x = v e l o c i t y o f b u s i n k m / h$ $(x + 20) \times 7 / 60 = (x - 20) \times 21 / 60 = d i s t a n c e b e t w e e n t w o b u s e s i n k m$ $(x + 20) \times 7 = (x - 20) \times 21$ $x = 40$ $\Rightarrow a n s w e r d)$ $d i s t a n c e b e t w e e n t w o b u s e s i s$ $(40 + 20) \times 7 / 60 = 7 k m$ $7 / 40 \times 60 = 13 \Rightarrow t h e b u s c o m e s e v e r y$ $13 m i n u t e s$
	Commented by Necxx last updated on 15/Nov/18

	$T h a n k y o u s o m u c h s i r$
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