Question

tim and elan are 90 km from each other.they start to move each other simultaneously tim at speed 10 and elan 5 kmph. if every hour they double their speed what is the distance that tim will pass until he meet elan

Answer 1

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the answer is 60
1st hour=tim 10kmph elan 5 the dist will be 90-15=75
2nd hr=tim->20kmph & elan->10 dist=75-30=45
3rd hr =tim->40 & elan->20..the totl dist for 3rd hr is 60.but we need only 45km to meet ..so we consider only 45mins instead of 3rd hr..
In 45mins =>tim ->30 & elan->15 
totl dist travld by tim is 10+20+30=60

Answer 2

hey there,

1. In the 1st hr they would've travelled = 5+10 = 15 miles. So, they are 75 miles apart (90-15 =75) at the end of 1st hour.

2. In the next 1 hour their speeds are 10 +20 = 30 m/hr(relative speed) and hence at the end of the 2nd hour they are 75-30 = 45 miles apart.

3. In the thrid hour their speeds are 20 + 40 = 60m/hr. They would meet each other at 45=60*t => t=3/4 of an hour or 45 minutes.

So, they have met each other end of 2hrs and 45 mins. 

Hope this helps!