Algebra Thinking Puzzle

G

Guest

Guest
Hello,

I was recently reading a lateral thinking book, and I came about this problem. I’ve been racking my brain trying to figure it out. Here is the problem

There are two glasses of equal size, glass A and B. A is empty and B contains some water. Half of glass B is poured into A. Once again, half of what is in B is poured into A. Once more, half of glass B is poured into glass A. At the end of 3 pourings, A is half full. How much water is left in B?'

Here is what I have so far...

Say X is the original amount of water in glass B

1/2X + 1/4X + 1/8X = 7/8 X

You see, however much water was in glass B to start, half is left after one pouring, a quarter is left after the second pouring and an eighth is left after the third pouring. So seven eights has been transferred.

..BUT WHAT DO I DO KNOW?? Please help me solve this sucker, and please show your steps algebraically (as best you can) and provide reasoning. Thanks!!

-Ryan
 
You know that (7/8)X=1/2 glass so
X=(8/7)(1/2) of a glass
Or
X=1/2 + (1/8)X
8X=4+X
 
Erm...

so 7/8X = 1/2 a glass

(8/7) 7/8X = (8/7) 1/2
cancels
out

X = 8/14
reduced...
X = 4/7

...did I follow you right? But I'm not sure that answers the puzzle-after the 3 pourings, how much water is in cup B?

Thanks so much for the help so far

Ryan
 
X=4/7 of a glass.
1/8th of X is left.
(1/8)(4/7) of a glass is left in B
My problem is I don't see any lateral thinking in either thread. Just algebra.
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Gene
 
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