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**sologuitar****Member**- Registered: 2022-09-19
- Posts: 467

A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80?

(A) 80

(B) 82

(C) 84

(D) 86

(E) 88

Can someone set this up for me?

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**Bob****Administrator**- Registered: 2010-06-20
- Posts: 10,476

Use 78 and 4 to find the total (T) for four tests.

Make an expression including x (the fifth score), T and the total for five tests.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

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**sologuitar****Member**- Registered: 2022-09-19
- Posts: 467

Bob wrote:

Use 78 and 4 to find the total (T) for four tests.

Make an expression including x (the fifth score), T and the total for five tests.

Bob

Sorry but I don't understand what you mean.

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**amnkb****Member**- Registered: 2023-09-19
- Posts: 253

sologuitar wrote:

A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80?

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**Bob****Administrator**- Registered: 2010-06-20
- Posts: 10,476

hi amnkb

Well done for being able to do so many of sologuitar's questions. But he has made it very clear that he wants hints and help rather than the whole answer. See, for example:

http://www.mathisfunforum.com/viewtopic.php?id=30204

If you do this, you deny him the chance of improvement by doing the work himself. I have suggested that you hide your answer and just include a hint. That provides maximum help because he is getting just the hint towards his own solution, and he has the opportunity to compare his answer with yours. I would be grateful if you would do this in future.

Meanwhile, I am going to exercise my job as an administrator by hiding your full answer.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

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**Bob****Administrator**- Registered: 2010-06-20
- Posts: 10,476

hi sologuitar

If you know a mean and the number of values then you can work out what the total was by reversing the calculation.

total = mean times number of values

You can do this twice; once where n = 4 and then again where n = 5

The difference between these two totals must be the 5th test score.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

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**sologuitar****Member**- Registered: 2022-09-19
- Posts: 467

Bob wrote:

hi amnkb

Well done for being able to do so many of sologuitar's questions. But he has made it very clear that he wants hints and help rather than the whole answer. See, for example:

http://www.mathisfunforum.com/viewtopic.php?id=30204

If you do this, you deny him the chance of improvement by doing the work himself. I have suggested that you hide your answer and just include a hint. That provides maximum help because he is getting just the hint towards his own solution, and he has the opportunity to compare his answer with yours. I would be grateful if you would do this in future.

Meanwhile, I am going to exercise my job as an administrator by hiding your full answer.

Bob

You are right, Bob. Solving my problems does not help me UNLESS I specifically seek the answer or work to be done it is best to let me play with the problem, right or wrong.

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**sologuitar****Member**- Registered: 2022-09-19
- Posts: 467

amnkb wrote:

sologuitar wrote:A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80?

Nicely-done but I am not learning. I am not thinking if you answer all my problems. There are questions that totally throw me in for a loop.

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