Latest self Aptitude Question SOLUTION: Having 2 sand glasses: one 7-minute and the second one 4-minute, how can you correctly time 10 minutes?

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(#M40008687) SELF question Minutes Keep an EYE

Having 2 sand glasses: one 7-minute and the second one 4-minute, how can you correctly time 10 minutes?

Vignesh (12 years ago)

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sowmya.B.J  (12 years ago)

let glass 1 take 7 min
glass 2 take 4 min
set the two glasses
after 4 min:glass 2 will b empty
glass1:leave it undistubed
glass 2:turn upside down
it takes 3 more min for glass 1 to become empty
after 7 min:glass 1 will be empty
glass1:leave it undistubed
glass2:turn upside down(it has completed 3 min now)
so after 3 min glass 2 will be emptied
4+3+3=10

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chaitanya  (12 years ago)

Turn both sand-glasses. After 4 minutes turn upside down the 4-min sand-glass. When the 7-min sand-glass spills the last grain, turn the 7-min upside down. Then you have 1 minute in the 4-min sand-glass left and after spilling everything, in the 7-min sand-glass there will be 1 minute of sand down (already spilt). Turn the 7-min sand-glass upside down and let the 1 minute go back. And that's it. 4 + 3 + 1 + 1 = 9

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