# Timing Puzzles

### Timing Puzzles

Timing Puzzle 1
Having 2 sand-glasses: one 7-minute and the second one 4-minute. How can you time correctly 9 minutes ?

Timing Puzzle 2
A teacher of mathematics used an unconventional method to measure a 15-minute time limit for a test. He just used 7 and 11-minutehourglasses. During the whole time he turned sandglasses only 3 times (turning both hourglasses at once count as one flip).

Explain how the teacher measured 15 minutes.

#### Vineet Patawari

Hi, I'm Vineet Patawari. I fell in love with numbers after being scared of them for quite some time. Now, I'm here to make you feel comfortable with numbers and help you get rid of Math Phobia!

## 12 thoughts to “Timing Puzzles”

1. saptarshi chaudhuri says:

STRT 7 N 11 MIN GLSSES SAME TYM..ATD D END OF 7 MIN FLIP 7 MIN GLASS N AT D EBND OF 11TH MIN FLIP THE 7 MIN GLASS AGAIN….DIS TYM WEN D 7 MIN GLAS EMPTIES TOTAL OF 15 MINS FINISH 15=7+4+4

2. saptarshi chaudhuri says:

START D 7 MIN N 4 MIN GLASS AT D SAME TYM ..AT D END OF 1ST 4 MIN TURN D 4 MIN GLS UPSYD DWN DEN AFTER 3MIN AS D 7MIN GLASS WILL EMPTY …TURN 7MIN GLS UPSYD DOWN AT THIS TYM 4 MIN GLASS HAS 1 MIN OF SAND LEFT ,AT D EMPTYIN OF 4 MIN GLS 8 MINS. TOTALLY HAS PASSED,NW 1 MIN OF SAND IS COLLECTED AT D DWNSYD OF 7 MIN GLS …JST TURN IT UPSIDE DWN AND BIT FINISHES D REMAINING 1 MIN OF 9 MINS…….:)

3. nishi says:

start both 7 min and 11 min sand glasses simultaneously.after getting filled 7min glass completely turn it upward down and simultaneously start to count time from now so that it counts 4 min untill we turn 11 min glass down for first time after it get filled completely. now count remaing time of 11 minutes untill the 11 min glass gets completely filled.it counts 4+11=15min.

4. nishi says:

start both the 7min and 4min clocks simultaneously.turn 4 min sand glass two times upward down after getting filled completely and simultaneously turn 7 min sand glass once after it get filled.here after getting filled the 4 min glass for third time, immediately start to count time from now for 7 min glass. turn down the 7 min sand glass after getting it totally filled.it will count 2 min. now turn down 7 min sand glass and count time till it get filled comlpletely, it counts 7 min.that total counts 2+7=9min.

1. uday says:

hi
if we can count 2 mins ten wats the problem with counting 9 mins!!!!

i tink ter should be some other way…….

5. ramani says:

start the 7 min glass..
after finishing 7 min glass..we are left to count only 2 min only(7+2=9)
so,half-fill the 4 min glass..it’s equal to 2 min right..!

6. response 2 time puzzle 1:

step 1: simultaneously start both the time glasses,wen 4 min are completed turn the 4 min sand glass so as to begin a new cycle(note:the other sand glass has 3 more min left i the first cycle)

step 2:wen 7 min sand glass completes its first cycle ten the 4 min sand glass will hav exactly the sand corresponding to one min (4-3=1)..from this point onwards start counting.

step 3:now after the second cycle of 4 min sand glass finishes,use it for 2 more cycles.thus u will be able 2 calculate 9 min!!!!

step 4: i.e 9 min=1 min from cycle 2 + 4 min from cycle 3+ 4 min from cycle 4..

7. knid says:

8. hey..you have hit bullâ€™s eye.. absolutely correct answer.

Here is the solution:

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

1. gurbir says:

really nic … do post me such questions.. i luv to solve dese..

9. Mohit says:

Start both sand glasses :

After 4 min., reverse the 4-min sandglass.

After 7 min., reverse the 7-min sandglass. 1 min will be remaining on 4-min sandglass. (Total time 7 min)

After 1 min., reverse the 7-min sandglass. So time remaining on the 7-min sandglass will be 1 min. (Total time 8 min)

Another 1 min., 7-min sandglass will be over. (Total time 9 min).