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Maths 9-1 GCSE Exam Style Question HELP!!

Can anyone guide me through the following question...

Pete records all his maths test scores.
Each score is a mark out of 100.

After 9 tests his mean score is 59
After 10 tests his mean score is 58.5
After 11 tests his mean score is 60
Work out the difference between his scores on the 10th and 11th tests.
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Avatar for Notnek
Notnek
21
Original post by NothingButWaleed
Can anyone guide me through the following question...

Pete records all his maths test scores.
Each score is a mark out of 100.

After 9 tests his mean score is 59
After 10 tests his mean score is 58.5
After 11 tests his mean score is 60
Work out the difference between his scores on the 10th and 11th tests.

After 10 tests his mean score is 58.5

Working backwards, what's his total score over the 10 tests?

After 11 tests his mean score is 60

Working backwards, what's his total score over the 11 tests?
Original post by NothingButWaleed
Can anyone guide me through the following question...

Pete records all his maths test scores.
Each score is a mark out of 100.

After 9 tests his mean score is 59
After 10 tests his mean score is 58.5
After 11 tests his mean score is 60
Work out the difference between his scores on the 10th and 11th tests.


Let's denote the sum of the scores from the first 9 tests by AA then we know that A9=59\frac{A}{9}=59 and so we have A=531A=531

Then for the 10 tests, we can say that he got bb amount of marks on the 10th test and so we get A+b10=58.5\displaystyle \frac{A+b}{10}=58.5 and you can work out bb itself - repeat similarly for the 11th test.

The reason for A+b is because A is the total of the first 9 tests, and b is the total of the 10th test, so adding these two together gives us the total of the first 10 tests which is what we want in order to get our mean score.
Original post by notnek
After 10 tests his mean score is 58.5

Working backwards, what's his total score over the 10 tests?

After 11 tests his mean score is 60

Working backwards, what's his total score over the 11 tests?


How can I work backwards because it is a mean so its an average..idk what the averages are
Reply 4
Avatar for Notnek
Notnek
21
Original post by NothingButWaleed
How can I work backwards because it is a mean so its an average..idk what the averages are

E.g. if the mean for 10 tests is 58.5 then to calculate this mean they must have divided the total score over the 10 tests by 10.

So if you work backwards, the total score must have been 585 because 585/10 = 58.5. Does this make sense?
Original post by RDKGames
Let's denote the sum of the scores from the first 9 tests by AA then we know that A9=59\frac{A}{9}=59 and so we have A=531A=531

Then for the 10 tests, we can say that he got bb amount of marks on the 10th test and so we get A+b10=58.5\displaystyle \frac{A+b}{10}=58.5 and you can work out bb itself - repeat similarly for the 11th test.

The reason for A+b is because A is the total of the first 9 tests, and b is the total of the 10th test, so adding these two together gives us the total of the first 10 tests which is what we want in order to get our mean score.


Perfect, Thanks for that, really appreciate it!
So b = 54
Then for the 11th...
\displaystyle\frac{531+54+c}{11} = 60
Hence, c = 75
Would the difference be 75?
(edited 7 years ago)
Original post by NothingButWaleed
Perfect, Thanks for that, really appreciate it!
So b = 54
Then for the 11th...
\frac{531+54+c}{11} = 60
Hence, c = 75
Would the difference be 75?


Is it true that 75−54=7575-54=75?
Original post by RDKGames
Is it true that 75−54=7575-54=75?


No it's 21,
oh so do I have to take away c from b?

Also, how do people get the fraction signs, and the root signs, etc??
Original post by NothingButWaleed
No it's 21,
oh so do I have to take away c from b?

Also, how do people get the fraction signs, and the root signs, etc??


bb is the score on the 10th test and cc is the score on the 11th test. To find the difference between 11th and 10th test scores you need to take one away from the other, so c−bc-b.

You're forgetting to use [tex]\text{
Unparseable latex formula:

}

in your LaTex formatting.
[QUOTE="RDKGames;70283422"]bb is the score on the 10th test and cc is the score on the 11th test. To find the difference between 11th and 10th test scores you need to take one away from the other, so c−bc-b.

You're forgetting to use [tex][/tex]inyourLaTexformatting.\text{[tex]}[/tex] in your LaTex formatting.

Oh ok so it is 21, many thanx for your help
12\frac {1}{2} it works thanx!
Original post by NothingButWaleed
Oh ok so it is 21, many thanx for your help
12\frac {1}{2} it works thanx!


No worries! :smile:
Original post by RDKGames
No worries! :smile:


Thanks!!! :biggrin:

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