# Thread: Help with this maths questions!

1. ## Help with this maths questions!

This seemingly elementary stats question stumped me. Anyone can help?

IN a test for eyesight, for which the scores vary from 0 to 6, the table below shows the distribution of these scores for some volunteers who took part in the test.

Score of < 2: 10 volunteers
Score of 2: 7 volunteers
Score of 3: 8 volunteers
Score of 4: x volunteers
Score of >= 5: 8 volunteers

If the mean score is 3, find the value of x.

The correct answer is 12.

maths whiz, fire away!

2. Originally Posted by Tweek
This seemingly elementary stats question stumped me. Anyone can help?

IN a test for eyesight, for which the scores vary from 0 to 6, the table below shows the distribution of these scores for some volunteers who took part in the test.

Score of < 2: 10 volunteers
Score of 2: 7 volunteers
Score of 3: 8 volunteers
Score of 4: x volunteers
Score of >= 5: 8 volunteers

If the mean score is 3, find the value of x.

The correct answer is 12.

maths whiz, fire away!
For score <2, use the midpoint of 0 and 1: 0.5
For score >=5, use the midpoint of 5 and 6: 5.5

Then use the formula Summation f(x) / Sum of x = 3

To help you further:

[0.5(10) + 2(7) + 3(8) + 4x + 5.5(8)] / (33+x) = 3

3. Originally Posted by canonsiao
For score <2, use the midpoint of 0 and 1: 0.5
For score >=5, use the midpoint of 5 and 6: 5.5

Then use the formula Summation f(x) / Sum of x = 3
that's right! I never did much of stats in my whole life of education, is this assumption of using the midpoint a standard practice?

4. Originally Posted by Tweek
that's right! I never did much of stats in my whole life of education, is this assumption of using the midpoint a standard practice?
That depends. Since no information of the distribution between 0 & 1 is given, you can generally assume that the 10 people are uniformly distributed between the two. Similarly for between 5 & 6. Sometimes more information about the distribution is known, so in those cases you cannot assume like this.

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