Question 815473: Bobby is counting forwards 1, 2, 3,... And at the same time and at the same speed, dawn is counting backwards x, x-1, x-2 ...... When bobby says the number 47, dawn says 83. What number did dawn start with?
Answer by Edwin McCravy(20060)   (Show Source):
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Bobby's number adds one each time, and Dawn's number subtracts 1 each time.
Therefore the sum of the numbers they are speaking is always the same.
Since the sum of their numbers is 47+83 = 130 at one particular time,
the sum of the numbers they are saying is ALWAYS 130. [To illustrate,
when Bobby says 48, Dawn will say 82, and 48+82=130. And when Bobby
said 46, Dawn said 84 and 46+84=130]
Therefore when Bobby said 1, Dawn had to say 129, because 1+129 = 130.
Edwin
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