Calculators and their uses

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Probability

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Can anyone explain what steps have been missed out here. I have a few calculators but none of them seem to have the same software or buttons are used by the author to show how this result was calculated using his calculator, which he does not share the make and model.

1 divided by 3 M+
1 divided by 4 M+
1 divided by 6 M+
divide M_RC =

That sequence is supposed to give the answer (1.3333)

I can't get this answer on any calculator I have. I do know from working it out on paper that it is correct.
 
I suspect the "M+" was an "add to whatever is in memory" key. That is, a running total is accumulated in memory, giving 1/3+ 1/4+ 1/6= 4/12+ 3/12+ 2/12= 9/12= 3/4. I'm not sure what "M_RC" would be but I do see that your answer, 1.333... is the same as 4/3, the reciprocal or 3/4.
 
HallsofIvy said:
I suspect the "M+" was an "add to whatever is in memory" key. That is, a running total is accumulated in memory, giving 1/3+ 1/4+ 1/6= 4/12+ 3/12+ 2/12= 9/12= 3/4. I'm not sure what "M_RC" would be but I do see that your answer, 1.333... is the same as 4/3, the reciprocal or 3/4.
Click to expand...
M_RC is probably memory recall.
 
HallsofIvy said:
I suspect the "M+" was an "add to whatever is in memory" key. That is, a running total is accumulated in memory, giving 1/3+ 1/4+ 1/6= 4/12+ 3/12+ 2/12= 9/12= 3/4. I'm not sure what "M_RC" would be but I do see that your answer, 1.333... is the same as 4/3, the reciprocal or 3/4.
Click to expand...
Yes I fully agree on paper it works out fine. The M_RC as lev888 posted and pointed out is a memory recall function but for the life of me I can't get the calculator to do this maths?

I'm assuming that the author is saying that he is adding these three fractions to three different memory slots in the calculator, but then says divide by M_RC = I either get the incorrect answer or a syntex error depending upon how I try to gain the answer. I'm sure there must be something incorrect about the method used?
 
Probability said:
Yes I fully agree on paper it works out fine. The M_RC as lev888 posted and pointed out is a memory recall function but for the life of me I can't get the calculator to do this maths?

I'm assuming that the author is saying that he is adding these three fractions to three different memory slots in the calculator, but then says divide by M_RC = I either get the incorrect answer or a syntex error depending upon how I try to gain the answer. I'm sure there must be something incorrect about the method used?
Click to expand...
M+ adds to the same memory slot. Then divide by M_RC gives you 1/(3/4).
Test: clear everything, 2, M+, ÷, M_RC, =. Do you get 0.5?
 
Probability said:
Can anyone explain what steps have been missed out here. I have a few calculators but none of them seem to have the same software or buttons are used by the author to show how this result was calculated using his calculator, which he does not share the make and model.

1 divided by 3 M+
1 divided by 4 M+
1 divided by 6 M+
divide M_RC =

That sequence is supposed to give the answer (1.3333)

I can't get this answer on any calculator I have. I do know from working it out on paper that it is correct.
Click to expand...
Did you mean:

1 divided by 3 M+
1 divided by 4 M+
1 divided by 6 M+
1 divide M_RC =

That missing 1 will throw you off.

I did not see the answer you got from your calculator. Please post that also.
 
Probability said:
Can anyone explain what steps have been missed out here. I have a few calculators but none of them seem to have the same software or buttons are used by the author to show how this result was calculated using his calculator, which he does not share the make and model.

1 divided by 3 M+
1 divided by 4 M+
1 divided by 6 M+
divide M_RC =

That sequence is supposed to give the answer (1.3333)

I can't get this answer on any calculator I have. I do know from working it out on paper that it is correct.
Click to expand...
I think you are saying that you don't have a calculator with an MRC button. According to one site I found, MRC means memory-recall-and-clear; when you press it once, it recalls the number in memory, and if you press it two times in a row, it clears memory. Calculators I'm familiar with that have these memory keys just have separate MR and MC. (The Windows calculator accessory is an example.) You just need MR here. But there's more going on.

Here's what the procedure is supposed to do, with the missing 1 inserted in the last line, and assuming the memory has been cleared first. (Without the 1 before the last division, no calculator would get their answer, I'm sure; and without clearing memory, all bets are off.)

1 ÷ 3 M+ : divides 1 by 3, put result 0.33333333 into memory​
1 ÷ 4 M+: divides 1 by 4, add result 0.25 to memory, changing it to 0.58333333​
1 ÷ 6 M+: divides 1 by 6, add result 0.16666667 into memory, changing it to 0.75​
1 ÷ MR = : recalls 0.75 from memory, divides 1 by 0.75, displaying 1.33333333​

But I did not get this result when I do it on the Windows calculator in standard mode, using MR for MRC. Instead, I get 1/13 = 0.0769230769230769.

That is because this calculator's M+ adds whatever is in the display to memory, so the memory just contained 3+4+6 = 13.

To get what they expect, I have to tell it to evaluate before each M+:

1 ÷ 3 = M+ : divides 1 by 3, add result 0.33333333 to memory​
1 ÷ 4 = M+: divides 1 by 4, add result 0.25 to memory, changing it to 0.58333333​
1 ÷ 6 = M+: divides 1 by 6, add result 0.16666667 into memory, changing it to 0.75​
1 ÷ MR = : recalls 0.75 from memory, divides 1 by 0.75, displaying 1.33333333​

You're right that this sort of calculation depends heavily on the particular calculator used, and it was foolish of that author to assume that everyone's calculator is identical. There is no standard.
 
Dr.Peterson said:
I think you are saying that you don't have a calculator with an MRC button. According to one site I found, MRC means memory-recall-and-clear; when you press it once, it recalls the number in memory, and if you press it two times in a row, it clears memory. Calculators I'm familiar with that have these memory keys just have separate MR and MC. (The Windows calculator accessory is an example.) You just need MR here. But there's more going on.

Here's what the procedure is supposed to do, with the missing 1 inserted in the last line, and assuming the memory has been cleared first. (Without the 1 before the last division, no calculator would get their answer, I'm sure; and without clearing memory, all bets are off.)

1 ÷ 3 M+ : divides 1 by 3, put result 0.33333333 into memory​
1 ÷ 4 M+: divides 1 by 4, add result 0.25 to memory, changing it to 0.58333333​
1 ÷ 6 M+: divides 1 by 6, add result 0.16666667 into memory, changing it to 0.75​
1 ÷ MR = : recalls 0.75 from memory, divides 1 by 0.75, displaying 1.33333333​

But I did not get this result when I do it on the Windows calculator in standard mode, using MR for MRC. Instead, I get 1/13 = 0.0769230769230769.

That is because this calculator's M+ adds whatever is in the display to memory, so the memory just contained 3+4+6 = 13.

To get what they expect, I have to tell it to evaluate before each M+:

1 ÷ 3 = M+ : divides 1 by 3, add result 0.33333333 to memory​
1 ÷ 4 = M+: divides 1 by 4, add result 0.25 to memory, changing it to 0.58333333​
1 ÷ 6 = M+: divides 1 by 6, add result 0.16666667 into memory, changing it to 0.75​
1 ÷ MR = : recalls 0.75 from memory, divides 1 by 0.75, displaying 1.33333333​

You're right that this sort of calculation depends heavily on the particular calculator used, and it was foolish of that author to assume that everyone's calculator is identical. There is no standard.
Click to expand...
Dr Peterson, I completely agree with the above. None of my calculators even trying to follow the instructions from their booklets will arrive at the correct answer. This takes me back to when I was an Uni some 17 years ago, I was in a Thermo-fluids lesson when I was advising the lecturer that my calculator results were inconsistent with his on the chalk board at that time. Turned out the solar powered calculator was at fault. However, in this example the calculators buttons are not the same exactly as the authors written example.

I've always said it and remain stead fast in it, that one must be able to work out the mathematical problem on paper before technology tells you what it wants you to believe is correct or not as the case may be!!

Thank you to all who replied.
 
Absolutely we should not be dependent on calculators.

The other side of that, which is more directly illustrated by this example, is that whenever you use a calculator, you need to know what it is doing. If you don't know how it will respond to a particular input, then it's like asking someone to help you when he doesn't know your language, and you don't know his.

And since calculators don't all speak the same language, you can never teach someone what to do without knowing what calculator he has, and being very familiar with that one.

May I ask, was there a 1 in the last line of the original that you accidentally omitted, or did you copy it exactly. I'd like to see the source.
 
Dr.Peterson said:
Absolutely we should not be dependent on calculators.

The other side of that, which is more directly illustrated by this example, is that whenever you use a calculator, you need to know what it is doing. If you don't know how it will respond to a particular input, then it's like asking someone to help you when he doesn't know your language, and you don't know his.

And since calculators don't all speak the same language, you can never teach someone what to do without knowing what calculator he has, and being very familiar with that one.

May I ask, was there a 1 in the last line of the original that you accidentally omitted, or did you copy it exactly. I'd like to see the source.
Click to expand...
Here is the source; This is all he wrote about using a calculator.
 

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There are, of course, several things wrong here: a probable typo in dropping the 1, a likely mistake in omitting = signs, the naivete of pretending all basic calculators are alike ...

I actually found the book online (probably illegally), and I see that it is a book that has been around for over 20 years, from a popular and trusted publisher. I see that the next example does have the 1!

I see that it says very little about calculators (only on these two pages), and introduces this section by saying, "This method uses an electronic calculator, commonly available at very low cost." That has a rather archaic feel to it! I imagine this bit probably dates back to the first edition and was never checked. (Why would a proofreader bother?)

I'm glad I don't work for a publisher.
 
Is it possible that the copy your looking at is an older version and my later copy (6) years old is another cut and paste of the older version maybe?

I would not like to be a publisher either as there are too many specialist areas of expertise for anyone person to grasp the understanding fully in this day and age.
 
The version I was looking at (6th edition) had a most recent copyright date of 2012, so they shouldn't be all that different; the problem you asked about is identical. I suspect it was never checked or changed, either for errors or for updating references to calculators. It is, after all, a trivial piece of the book.
 
Sorry for the mega late reply. His books are fantastic overall but as a learner it just gets upsetting when we can't get to the bottom of a problem and I don't like moving forwards until I've understood a problem. That is just me.

I'd like to point out now that the calculator I have the casio fx-85GT PLUS will solve these problems.

1 divided by 3 M+
1 divided by 4 M+
1 divided by 6 M+
1 divided by ALPHA M = 1.33333.....

I can't find the information in the guide booklet above which I've now been advised from Casio
 
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