Blog # 73 : The hourglass

You have two sand hourglasses, one that measures exactly 4 minutes and one that measures exactly 7 minutes. You need to measure out exactly 2 minutes. Using only these two hourglasses, how can you measure out exactly 2 minutes ? Click here to see the solution. p.s. - For Remarks please hit the given link once. For Hint, hit it twice and for the solution, hit it thrice. Remarks: No remarks. Hit again for hints. Hints: Just think what type of actions can be responsbile for such result? Hit again for solution. Solution: 7x - 4y = 2 we have a simple soultion, x=2 and y=3 We have 7*2 - 4*3 = 2 So we start both simultaneously. When 4 completes invert it, next invert 7 when done, next invert 4 when done again twice. Time remaining for 7 to finish is 2 minutes now.