Math CentralQuandaries & Queries


Question from sunjoo, a parent:

a friend tells you to think of a 5-digit whole number. then do the following in order : multiply the number by 2. add 200 to the result. divide the result by 2. subtract 100 from the result. what is the greatest number you can get as an answer?

Hi there.

Let n = the 5 digit whole number.

"multiply the number by 2"

That's 2n.

"add 200 to the result"

That makes 2n + 200.

"divide the result by 2"

That makes (2n + 200) / 2 = n + 100.

"subtract 100 from the result."

That makes n + 100 - 100 = n, the original number.

"what is the greatest number you can get as an answer?"

That would be the greatest number that satisfies the original constraints on n. It is a five digit whole number, so what is the greatest one of those?


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