Puzzle 689
What number comes next in this sequence:
302 · 202 · 102 · 002 · 991 · ?
Puzzle Copyright © Kevin Stone
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Hint
Try reversing the numbers.
Answer
891.
If we reverse each of the numbers we get:
203 · 202 · 201 · 200 · 199 · ?
Which is counting down from 203, and the next number is 198, which is 891 when reversed.
Puzzle 690
In my money box, I found $36.80 made up of equal numbers of quarters, dimes, and nickels.
How many of each coin did I find?
Puzzle Copyright © Kevin Stone
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Hint
Remember that a quarter is 25c, a dime is 10c and a nickel is 5c.
Answer
92 of each coin.
Reasoning
There are an equal number of quarters, dimes and nickels, so we know that the answer must be a multiple of:
25c + 10c + 5c = 40c
and:
3680c ÷ 40c = 92 coins.
Puzzle 691
What number comes next in the sequence:
11 · 13 · 17 · 31 · 37 · 71 · 73 · 79 · 97 · ?
Puzzle Copyright © Kevin Stone
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Hint
A very tricky puzzle involving prime numbers.
Answer
101.
These are prime numbers, which, when reversed, are also prime.
Puzzle 692
How much soil is there …
… in a circular hole 2 metres deep and 1 metre across?
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Hint
How much soil is in any hole?
