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Friday Riddle Answer

nudgie's picture
nudgie
Posts: 1483
Joined: Sep 2006

RIDDLE:A certain investment doubles Joe's money every five years. If Joe leaves all the money invested, in 40 years he'll have 384,000. How long will it take to have $340,000 if he starts with twice as much money? How much money did he start with?

ANSWER: It would take 35 years if he invested twice as much. Think of it this way; in the first scenario he has twice as much in 5 years, leaving 35 more to reach $384,000. He started with $1,500. This is basic algebra: 384,000 = x (original investment) + 2x + 4x + 8x + 16x + 32x + 64x + 128x or 256x, thus 384,000/256 = 1,500.

PGLGreg's picture
PGLGreg
Posts: 741
Joined: Jul 2006

In May, after a rather easy riddle from Nudgie, I thought you all might still have some puzzle-energy left over, and I posted the following, which is a variation of this week's puzzle:

The water lentil reproduces by dividing into 2 every day. Thus on the first day we have 1, on the second 2, on the third 4, on the fourth 8, and so on. If, starting with one lentil, it takes 30 days to cover a certain area, how long will it take to cover the same area if we start with 2 lentils?

nudgie's picture
nudgie
Posts: 1483
Joined: Sep 2006

Now you are going to make me go out a find a really hard and complex riddle book

PGLGreg's picture
PGLGreg
Posts: 741
Joined: Jul 2006

I didn't mean to be saying this riddle was too easy --- rather, that the previous one from May was. I repeated the Water Lentil riddle just because I thought you'd find the similarity between the puzzles interesting.
--Greg

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