You are Here: Home >< Maths

# S2 Jan 2003 Question 1 Watch

1. Hi there,

I am a gap year student and therefore have no support from any teacher.

Question 1:

1. An engineer measures, to the nearest cm, the lengths of metal rods.

(a) Suggest a suitable model to represent the difference between the true lengths and the measured lengths.

--

I understood that it was a uniform distribution but I'm not sure where they get the answer to part a from, that U[-0.5, 0.5]..

I must be having a dim moment, as nobody else on the internet seems to have struggled with this question.

Why is U[-0.5, 0.5]?

Thanks for any help in advance!
2. (Original post by kelsey.phillips)
Hi there,

I am a gap year student and therefore have no support from any teacher.

Question 1:

1. An engineer measures, to the nearest cm, the lengths of metal rods.

(a) Suggest a suitable model to represent the difference between the true lengths and the measured lengths.

--

I understood that it was a uniform distribution but I'm not sure where they get the answer to part a from, that U[-0.5, 0.5]..

I must be having a dim moment, as nobody else on the internet seems to have struggled with this question.

Why is U[-0.5, 0.5]?

Thanks for any help in advance!
YOu will round the real fraction to the nearest whole number (x) within this range (x-0,5, x+0,5)
3. (Original post by ztibor)
YOu will round the real fraction to the nearest whole number (x) within this range (x-0,5, x+0,5)
Sorry but that still doesn't make sense to me?

the real difference could be 0.3, then 0.3+0.5 =0.8??
4. (Original post by kelsey.phillips)
Sorry but that still doesn't make sense to me?

the real difference could be 0.3, then 0.3+0.5 =0.8??
No. The real difference could be between -0.5 and +0.5
When the true length is X the mesured length is x' then

[X-x'|<=0.5

for greater difference you should to round a greater or smaller integer value than X

So U(-0.5,0.5) the uniform distribution for the difference and not for
the length
5. (Original post by ztibor)
No. The real difference could be between -0.5 and +0.5
When the true length is X the mesured length is x' then

[X-x'|<=0.5

for greater difference you should to round a greater or smaller integer value than X

So U(-0.5,0.5) the uniform distribution for the difference and not for
the length
I don't understand why the difference necessarily has to be between -0.5 and +0.5?

Have I missed something? Why couldn't the difference be 0.8?

6. (Original post by kelsey.phillips)
Hi there,

I am a gap year student and therefore have no support from any teacher.

Question 1:

1. An engineer measures, to the nearest cm, the lengths of metal rods.

(a) Suggest a suitable model to represent the difference between the true lengths and the measured lengths.

--

I understood that it was a uniform distribution but I'm not sure where they get the answer to part a from, that U[-0.5, 0.5]..

I must be having a dim moment, as nobody else on the internet seems to have struggled with this question.

Why is U[-0.5, 0.5]?

Thanks for any help in advance!
Imagine the true lengths are

4.49
12 and
6.52

The measured lengths are then
4
12 and
7

The differences are then
0.49
0 and
-0.48
7. (Original post by kelsey.phillips)
I don't understand why the difference necessarily has to be between -0.5 and +0.5?

Have I missed something? Why couldn't the difference be 0.8?

Because the 0.8 difference means 0.2 difference from the next/previous integer value
and we will round to that value, so the difference will not be 0.8.
8. (Original post by BabyMaths)
Imagine the true lengths are

4.49
12 and
6.52

The measured lengths are then
4
12 and
7

The differences are then
0.49
0 and
-0.48

(Original post by ztibor)
Because the 0.8 difference means 0.2 difference from the next/previous integer value
and we will round to that value, so the difference will not be 0.8.
I'm not sure the explanation is coming across clearly on computer.. but I think you are trying to say:

As the measured value will be an integer that we have rounded up or down to, we take the difference to be 0.5 or -0.5?

How do we know that the measured value will be an integer value?

Thanks!
9. (Original post by kelsey.phillips)
How do we know that the measured value will be an integer value?

Thanks!
Your question says "An engineer measures, to the nearest cm, the lengths of metal rods."

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 21, 2014
Today on TSR

### I don't drink alcohol...

Is freshers still worth it?

### Girlfriend wants me to make her cry...

Discussions on TSR

• Latest
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams