The author blog of C. J. Ivory

Tinkerer with words. Dresser-Upper. Adorer of Steampunk and VictoriaNoir fiction. Occasional Lawgineer.

February 14, 2011

Tuesday Tangle: Lose Ten Brain Cells in Nine Minutes a Day!

Gentle Reader,

This week's tangle is dedicated to the amazing strength of will that stopped me from succumbing to an infomercial yesterday. Said infomercial featured the *amazing* Ab-Circle Pro. They were on special! Everyone on the ad was so thin! And they promised me masses of weight loss in just three minutes a day. Three minutes a day. Heck, even I have that kind of time lying around. 

However, just as I was reaching for the phone, the rational side of my brain spoke up (which was a damn-near miracle, since I could swear I'd left it chained to a radiator somewhere). So, long story short: I'm still as flabby as ever, but I'm loving that bonus three minutes a day that I don't have to exercise.

And what did I use today's three minutes for? Why, to furnish you with this week's tangle, of course...

Lose Ten Brain Cells in Nine Minutes!

Tanya is a sucker for TV infomercials. Her latest purchase is an exercise machine which, the sellers claim, will enable her to lose 10 pounds in one week. All she needs to do - so they say - is use the machine for nine continuous minutes each day.

On the first day, an enthusiastic Tanya throws on her track pants and searches the house for a timer. But all she can find is two old fashioned egg timers. The smaller egg timer takes four minutes for the sand to go through, while the bigger takes seven minutes for the sand to go through.

If Tanya cannot stop or slow down the sand while it is falling through the egg timers, how can she know when she has been exercising for nine minutes? (Presume that Tanya is able to flip the egg timer without getting off the machine, so it doesn’t interrupt her exercise.)

(Solution below)

Solution: Tanya starts both egg timers at the same time, and begins exercising.
At the four-minute mark she turns the smaller egg timer over. She has been exercising for four minutes.
At the seven minute mark, she turns the large egg timer over. She has now been  exercising for seven minutes.
At the eight minute mark, the small egg timer needs turning. But instead, Tanya turns over the large egg timer. Because it had been running for only one minute, when she turns it over, the sand in the large egg timer runs for exactly another minute in the other direction. At the end of this minute, when the large egg timer is finished, Tanya has been exercising for nine minutes.


Cathy said...

Yay, got it! Reminds me of the water jug problem from Die Hard 3. I watched that movie for the first time on DVD and had to pause it and solve the problem before I'd let my husband finish watching.

Charlotte Jane Ivory said...

Well done, Cathy! I think I know the water jug one too; it's a goodie. Do you know, I think there is an alternate way to solve this one, so I wonder if anyone will come up with it...