## Search This Blog

### Hour Glass Riddle

Hour Glass Riddle - 19 July

You have two hour glasses one measure 7 minutes and other measure 4 minutes.
Using these two hour glasses, you need to measure exactly 9 minutes.

How come ?

1. name 7 mins hour glass A and 4 mins one B.
start both of them, as soon as B gets empty. reverse it. by now 4 mins are noted. when you reverse B, you have 3 mins in A. at the lapse of 3 mins A gets empty and 1 min is left in B. mark the point of one min on both the bulbs of B glass. now you can easily get two mins out of B hour glass.
thank you.

2. start both the hourglasses
when the small one finishes, turn it down (4 min)
when the big one finishes, turn it down (7 min)
when the small one finishes, turn the big one down (8 min)
now the big one will finish in 1 min and total time 9 mins..

3. Correct another approach,
start both hourglasses, name 7 mins hour glass A and 4 mins one B.
once 4 min is over turn B down.
Once A is over B is left with 1 min.
turn both down, by the time B is over -3 mins
Turn both down, A will take 3 minutes to finish - 3 mins
Again turn both Now B will take 3 mins.

4. Very easy do it physically .......but tricky to explain

5. Name 7min as A
4 min as B.

1) Start by turning down both A and B
2) When B completes, we will have (7min-4min) in A
3) That is the first three minutes
4) Then turn A (which has 3 mins), this will be the second 3 mins
5) Repeat (1) for the next 3 mins
6) Totally we will have 3+3+3 mins

6. Turn down 4 mins (A) and 7 mins (B) hourglass together.
When A is empty invert A and start recording time.
3 mins recorded.

Now you'll have 1 min in A and 7 mins in B).
Invert both, when A is empty B will have
6 mins.
6+3=9