Why can any fraction whose denominator has only 2s and 5s in its prime factorization can be written as a terminating decimal?

Any number you can divide by 2 or divide by 5 terminates (does not repeat).

.... Thinkpads_User

A denominator of 10^n has only 2s and 5s in its prime factorization.

If this is a 7th grade problem, I assume that naseeam wants a very simple answer as first provided. ... Thinkpads_User

"Why can any fraction whose denominator has only 2s and 5s in its prime factorization can be written as a terminating decimal?"
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To be perfectly correct you must define "fraction" a bit narrower.
9/3 terminates

3 does not have only 2s and 5s in its prime factorization, so whether 9/3 terminates is irrelevant.

"3 does not have only 2s and 5s in its prime factorization, so whether 9/3 terminates is irrelevant. "
true
But it is relvant when considering the converse (I know, that was not asked)

All covering the same ground over and over again here.

.... Thinkpads_User

... Thinkpads_User said

"All covering the same ground over and over again here."   Not quite

you said
"Any number you can divide by 2 or divide by 5 terminates (does not repeat). . "

but that is not really an answer to the question asked (which was Why?

furthermore consider a number (you said ANY number so try 1/3)

(1/3)/2 = 0.16666666....

does not terminate.   so at best you have to expand your answer a bit.
The other answers tried (and eventually did) answer the why?

.

Touche.  I meant and should have said any non-repeating number divided by 2 or 5 will terminate and not repeat. Carelessness on my part.

... Thinkpads_User