A B C D want to get across a lake 312 miles across.
Swimming speeds in mph: A=4 B=8 C=12 D=16
They have a motorboat that goes at 48mph but this boat can only take 2 persons.
D leaves first; 2 hours later the other 3 leave.
During the last hour, a strong salmon decides to push the boat. This causes the boat to go 72mph during the last hour.
All 4 arrive on other side at same time, 16 hours after D left.
How many miles did the boat travel?
For how many hours did A swim?
How many miles did C swim?
How many hours was B in the boat?

• Nice puzzle.
  
  First of all D left for swimming @ 16 mph.
  For 15 hours he swam (15*16= 240 miles) and went by boat for last 1 hr (72 miles).
  C starts swimming @ 12 mph after 2 hrs.
  Also A and B leave by Boat for 5 hrs ( covered 48*5= 240 miles).B swam further for 9 hrs to cover 9*8=72 miles, total 312 miles.
  A came back by boat for 3 hrs and catches C who has covered 8*12=96 miles.
  For next 4 hrs, A and C covered 4*48= 192 miles and reached 96+192=288 miles point from start. C starts swimming again for 2 hrs and covered balance 24 miles.
  A comes back for 1 hr covering 48 miles and reaches (288-48=240) miles point to catch D who has covered 15*16=240 miles in 15 hours.
  In last 16th hour, A and D covered 72 miles ( at faster speeeeeeeeeed)in 1 hr and all A,B,C,D reached on the other side at same time.
  
  Based on this
  
  boat travelled for all the time i.e. 14 hours(16-2) .. no doubt.
  A swam for ZERO (0) hours.
  D swam for 15 hours.
  B was in boat for 5 hours.
• 12 years agoHelpfull: Yes(3) No(0)
• How many miles did the boat travel?...... 696 miles (48*13 +72*1)
  For how many hours did A swim?............. Zero (0)
  How many miles did C swim? .............. 120 miles
  How many hours was B in the boat? ........ 5 hours
• 12 years agoHelpfull: Yes(3) No(0)