After a 5% discount, a telephone bill is $79.50. How much was the bill originally?
1 answer:
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Since <em>N</em>/2 leaves a remainder, <em>N</em> must be odd and ends with 1, 3, 5, 7, or 9.
<em>N</em>/5 also leaves a remainder, so <em>N</em> is not divisible by 5, so it does not end in 5.
The only correct choice is then 9, since
1 = 0•5 + 1 and 1 = 0•2 + 1
3 = 0•5 + 3 and 3 = 1•2 + 1
7 = 1•5 + 2 and 7 = 3•2 + 1
9 = 1•5 + <u>4</u> and 9 = 4•2 + <u>1</u>
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Alternatively, the given information is equivalent to saying
Then you can use the Chinese remainder theorem to find <em>N</em>.