\[It\ is\ a\ well\ known\ fact\ that\ if\ in\ a\ fraction,the\ denominator\ is\ of\ the\ \\ form\ 2^{m}*5^{n}\ where\ m\ and\ n\ are\ non-negative\ integers\ the\ fraction\ \\ has\ a\ \\ terminating\ decimal.\] \(Here\ is\ the\ proof:\) \(Let\ us\ say\ that\ there\ is\ a\ fraction\ in\ which\ the\ numerator\ is\ N\ and\ \\ the\ denominator\ be\ 2^{m}*5^{n}\ where\ m+n=x\) \(The\ fraction\ can\ be\ written\ as:\\ \dfrac{N}{2^{x-n}*5^{x-m}}\) \(Multiplying\ by\ \dfrac{2^{n}}{2^{n}}\ and\ then\ by\ \dfrac{5^{m}}{5^{m}}\\ we\ have\ a\ fraction\ which\ has\ a\ new\ numerator,let\ us\ call\ it\ A.\)\ \(The\ new\ denominator\ is\ 10^{x}\\ Thus,the\ new\ fraction\ is\ \dfrac{A}{10^{x}}.\)\ \(Which,obviously,has\ a\ terminating\ decimal\ expansion.\)

## Comments

Sort by:

TopNewestexpect the unexpected ! – Raven Herd · 10 months, 4 weeks ago

Log in to reply

It is a very simple proof which was in my RD SHARMA but I thought it too elegant not to share it with you guys. – Adarsh Kumar · 2 years, 1 month ago

Log in to reply

Nice note, Adarsh. You may also like to add the number of decimal digits after a number of such a form terminates. It's closely related to your proof. Also, you don't need to latex the whole thing. If you are using a latex editor, then there's no need. If you want to learn it, you can easily do so here. Thanks. – Satvik Golechha · 2 years, 1 month ago

Log in to reply

– Adarsh Kumar · 2 years, 1 month ago

Do you have the proof of the property of recurring decimal expansions that they repeat for n-1 digits in a fraction 1/n?Log in to reply

– Satvik Golechha · 2 years, 1 month ago

That's not necessary. It is only true in case of cyclic numbers. I was referring to the number of after-decimal digits after \(\frac{x}{2^m5^n}\) terminates. It's the larger of \(m\) and \(n\).Log in to reply

– Adarsh Kumar · 2 years, 1 month ago

hmmmLog in to reply

– Adarsh Kumar · 2 years, 1 month ago

thanx.But I recently learned LATEX and now I can't get enough of it.Log in to reply

– Satvik Golechha · 2 years, 1 month ago

I don't understand "I can't get enough of it", you can always learn it. It's really easy to learn.Log in to reply

– Adarsh Kumar · 2 years, 1 month ago

"I can't get enough of it" means now I can't resist writing it.It is an idiom,I think.Log in to reply

– Adarsh Kumar · 2 years, 1 month ago

BTW which class r u in?Log in to reply

– Satvik Golechha · 2 years, 1 month ago

I'm in class 10.Log in to reply

– Adarsh Kumar · 2 years, 1 month ago

oh,ok.Log in to reply

@Krishna Ar – Adarsh Kumar · 2 years, 1 month ago

Log in to reply

– Krishna Ar · 2 years, 1 month ago

(y)Log in to reply

@Krishna Ar, this is called popularity! – Satvik Golechha · 2 years, 1 month ago

WOWLog in to reply

– Krishna Ar · 2 years, 1 month ago

-_-Log in to reply

– Adarsh Kumar · 2 years, 1 month ago

heheLog in to reply