How to calculate sum?

Question

As you can see in my screenshot, I take 25% from score and sum the result which come up to 64. My question is that how can I obtain the same 64 from sum of full(175) and score (144)? I have tried something like 144*25*3/175, but I got 62. How can I get the exact 64 here?

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I am sorry, your question is not clear to me. What exactly are you asking? — LASV, Dec 02 '13 at 07:14
@user2369284, In fact I am not good in Maths, but desire to explore. I have tried all the ways I thin possible to find out this solution. But I believe there must some powerful formula or solution to this problem.... — Mawia HL, Dec 02 '13 at 07:23
@MawiaHL Either we are misunderstanding you or you are confused. 22 is not 25 percent of 44. None of your percentages make sense. — LASV, Dec 02 '13 at 07:24
@Luis, I am taking 25% from 50. 50 is fullmark, 44 is score mark, so in order to take 25%: 44/50*25=22 — Mawia HL, Dec 02 '13 at 07:27
The way you have worded the question is not clear (In my opinion). — LASV, Dec 02 '13 at 07:35
If you look at the screenshot carefully, you can see that sum up full which is 175, sum of score is 144. And I take out 25% from each subject which total is 64. And All I want is to find out how can we obtain 64 from 175 and 144. — Mawia HL, Dec 02 '13 at 07:40

score 1 · Accepted Answer · answered Dec 02 '13 at 07:39

1

In principle, it cannot be done. Imagine two situations, one test out of $50$, the other out of $100$.

Case A: You got $50$ on the first test, $25$ on the second. Then the total score is $75$ out of $125$.

Case B: You got $25$ on the first, and $50$ on the second. Again the total score is $75$ out of $125$.

Now let us in each case do your "$25\%$" calculation. On A, you get $25$ on the first, $6.75$ on the second, total $31.75$.

On B, you get $12.5$ on each, total $25$.

Note that on each of scenarios A and B, total achievable scores were the same, and total actual scores were the same. But the "$25\%$" calculations yielded quite different numbers. So we cannot recover the "$25\%$" result just from total score achievable and total score achieved.

answered Dec 02 '13 at 07:39

André Nicolas

507,029

I think you have mistaken my question. As I am not good in English, it is difficult to say what I want in appropriate terms. On the first test I got 44 and full mark is 50, and if I take 25% from it, it becomes 22. And there are two more tests. The total of all the tests come down to the total row at the bottom of the table, which in the fullmark column is 175 and score column 144. So by making use of the available information and 175 and 144, can we achieve 64 which is sum of 25% of mark we got from each test. Thanks in advance. – Mawia HL Dec 02 '13 at 07:52
My understanding of your calculation for this case is that your $44$ out of $50$ was $88%$, and you took $25%$ of that, getting $22$. My example used two tests instead of three just to simplify the arithmetic. One can produce similar examples with three tests. – André Nicolas Dec 02 '13 at 07:57
got it. thank you. So does it mean what I want to achieve is impossible? – Mawia HL Dec 02 '13 at 07:59
Yes, it is not possible. If the achievements are roughly similar, that is, the percentages you got on the various tests don't change too much, you can get a good estimate just from the total achievable and the total scores achieved. – André Nicolas Dec 02 '13 at 08:05
thank you very much for taking your time while I have no enough reputation to upvote your answer. I just found that if all total marks are the same, it can be achieved. – Mawia HL Dec 02 '13 at 08:27
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You are welcome. If you mean with $3$ marks rather than $2$, it will not be true. Just add to scenarios A and B a third test out of $100$ in which, in both scenarios, you get $0$, or more generally the same matk. – André Nicolas Dec 02 '13 at 12:18

How to calculate sum?

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