80 coins are placed in a straight line on the ground. The distance between any 2 consecutive coins is 10 feet. How far must a person travel to bring them one by one to a basket placed 10 feet behind the first coin?
a)64800
b)68400
c)86400
d)46800
e)48600

• a)64800
  Explanation:
  Basket is 10 feet behind first coin.To take first coin a person has to travel 20ft(10+10) to and fro.Similarly,to collect second coin he has to travel 40ft (20+20) to & fro.This forms an A.P series.T0 collect last coin he has to travel 1600ft(800+800)
  
  (10+10)+(20+20)+..............+(800+800)
  =20+40+60+80+......+1600
  
  Sum of n terns in A.P is n(a1+an)/2.
  
  hence Sum of first 80 terms =80(20+1600)/2
  =64800
• 8 years agoHelpfull: Yes(7) No(0)
• to take first coin we need 10 feet then second coin (10+10)=20.......
  10+20+30+...................+(80*10)
  =80/2(2*10+(80-1)*10)
  =32400ft
• 8 years agoHelpfull: Yes(0) No(3)