# How to calculate proportions on a FX-300ES Plus 2nd edition

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### #1 calc-lover

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Posted 14 June 2024 - 10:52 PM

What are the key presses to solve the following proportion:

3/2 = 6/x

I know that the answer is:  x=4

And I know that to solve the proportion would be:  3x = 2*6 ..... x = 12/3 ..... x=4

But I would like to learn how to enter the problem on the FX-300ES directly.

Is there a way to do it on the FX-300ES Plus?

### #2 calc-lover

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Posted 16 June 2024 - 06:07 PM

OK, apparently the FX-300ES Plus cannot solve the proportion (ratio) problem directly.

What is the cheapest Casio calculator that can solve proportions directly?

### #3 loklol

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Posted 19 June 2024 - 01:29 AM

I think you may want the fx 570 vn plus, because thats the only calc that i know has the ratio mode, but it's probably better to get 83/5 GTX as it has ratio mode.

### #4 Steveyboi

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Posted 19 June 2024 - 02:05 AM

OK, apparently the FX-300ES Plus cannot solve the proportion (ratio) problem directly.

You can do it, if you know the right formula. For A/B = C/x, you would do (B*C)/A to get x.

In your provided proportion x would be (2*6)/3 = 12/3 = 4.

This is called the rule of three, it appears that it is not taught in most countries but it is taught here in Vietnam. It's very useful when solving a proportion with just a single unknown, and it's faster than standard cross-multiplication.

Edited by gwetm, 19 June 2024 - 02:13 AM.

### #5 calc-lover

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Posted 19 June 2024 - 06:47 PM

You can do it, if you know the right formula. For A/B = C/x, you would do (B*C)/A to get x.

In your provided proportion x would be (2*6)/3 = 12/3 = 4.

This is called the rule of three, it appears that it is not taught in most countries but it is taught here in Vietnam. It's very useful when solving a proportion with just a single unknown, and it's faster than standard cross-multiplication.

I posted the method to solve for "x" in my original post.  But that required me to write down the ratio on paper to get x=(2*6)/3 and then for a more complicated values, use a simple calculator to find the value of x.  ANY calculator can solve for x.

Since I find reason to solve proportions (ratios) fairly regularly, I wanted a calculator that would allow inputting the ratios directly without using paper to visualize the actions required.  Unfortunately, it appears that the FX-300ES Plus cannot do this simple calculation directly.

Wonder if the FX-991ES Plus 2nd edition can do it directly?

Edited by calc-lover, 19 June 2024 - 06:53 PM.

### #6 calc-lover

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Posted 19 June 2024 - 07:04 PM

I think you may want the fx 570 vn plus, because thats the only calc that i know has the ratio mode, but it's probably better to get 83/5 GTX as it has ratio mode.

Thank you very much for your suggestions.

Looking at  the FX-83 GTCW on Amazon, I see that the menu shows the ratio function.  Excellent!  But I don't see a memory +/-/recall on the keyboard.  I use the memory functions regularly also.

### #7 calc-lover

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Posted 19 June 2024 - 07:44 PM

HAVE YOU USED THE 570MS OR 991MS

No, I have not.

### #8 Steveyboi

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Posted 24 June 2024 - 06:33 AM

Wonder if the FX-991ES Plus 2nd edition can do it directly?

Hmm, don't think so. It doesn't have a Ratio mode. If you're going for a cheap option, then yeah, the fx-83/85GT X would be a good fit.

If you want a high-end, the fx-570VN PLUS should do it.

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