Father and both of his sons decided to visit their grandmother who lives 33 km away from city. They will be using a moped to get there. The speed of moped is 25 km/h and 20 km/h with passenger (You can't carry 2 passengers at the same time.) Both sons can walk at 5km/h.
Prove that all of them will reach grandma's house within 3 hours.

Question

anonymous · Answer

Father and one son will go first and another son will walk.
So one trip Father + One Son at a speed of 20km/hr will cover 33km in 1 hr 9 min
then father will return at a speed of 25 km/hr.
mean while another son has covered 5.75km in 1 hr 9 min
then father and another son are 33-5.75 km = 27.25 km apart after 1hr 9 min
father will start moving @ a speed of 25km/hr and son will start moving towards his father @ a speed of 5km/hr
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you have to find out at what point they will meet