Four people need to cross a rickety bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without one. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge. Times for each person: 1 min, 2 mins, 7 mins and 10 mins. What is the shortest time needed for all four of them to cross the bridge?

• Shortest time will be 7 minutes.
  let a will take 1 min
  b = 2 mins
  c = 7 mins
  d = 10 mins
  first a will go with b;time taken=2mins,
  a will return=1min;
  then c will go with d, time taken=10mins;
  be careful here for shortest time, b will return; time taken= 2mins
  now a & b will go, time taken=2mins
  so shortest time =(2+1+10+2+2)
  =(17 minutes) Ans
• 11 years agoHelpfull: Yes(3) No(0)
• let a take 1min
  b take 2mins
  c take 7 min
  d take 10 mins,
  first a will go with d;time taken=10mins;
  a will return=1min;
  then a will go with c,time taken=7 mins;
  again a will return=1 min and come with b=2 mins;
  so toatl time taken=10+1+7+1+2=21 mins
• 11 years agoHelpfull: Yes(0) No(2)