Can you answer this riddle?

[Chloe]

If you have two hourglasses -- one four-minute timer and one seven-minute timer, how can you measure nine minutes?

 

[sandra]

seven-minute timer + half of the four-minute timer

 

[boomn4x42]

Turn both over at once.

When the 4 min glass empties turn it over, let the 7 min timer keep going.

When the 7 min glass empties turn it over.

When the 4 min glass empties again, 8 minutes would have passed and there will have been 1 min of sand passed in the 7 min timer, so turn the 7 min timer back over to get 9 minutes.

 

[StarGirl]

do the seven minute timer then half the four minute timer...?

 

[Rebecca T]

use a stopwatch instead

 

[Evil!!!]

turn em on on the same time
when the 7 minute timer is over and the 4 minute timer is half way through

7 + 1/2 of 4
7+2=9