The puzzler on Car Talk on KQED was kind of fun today. Turns out it was an old episode. So it's not this weeks puzzler.
A guy walks into his friends barber shop and gets a cut. He asks his friend, the barber, how much it is and the barber responds that it's free. They argue for a little bit and the barber decides that the friend can go to the register, double the amount in the register, then subtract $20 and leave that amount. The friend does that and another customer comes in.
The barber does that cut and tells that customer to do the same thing. Double the amount in the register, subtract twenty and leave that amount.
Another customer comes in and does the same thing. Then one more. Then a fifth customer, and when he goes to the register he says he can't do it, because there is nothing in the register.
The question is, how much was in the register to start with that would have the register get down to zero on the fifth customer.
Anyway, I figured it out, so I'll post the answer in a couple of days. Feel free to put the answer in the comment on this post if you can figure it out in the meantime.
2(2(2(2x-20)-20)-20)-20=0
solve for x
2(2(4x-60)-20)-20=0
2(8x-140)-20=0
16x-300=0
16x=300
x=18.75
The trick is in realizing the register is equal to zero when the 4th guy leaves and everyone is taking money out and not adding it in.
Posted by: Mr Wizard at April 19, 2004 12:13 PMThanks for signing in, . Now you can comment. (sign out)
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