# S2 revision help!

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#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.

(b) Find the probability that for a randomly chosen rod the measured length will be within 0.2 cm of the true length.

Two rods are chosen at random.
(c) Find the probability that for both rods the measured lengths will be within 0.2 cm of their true lengths.
0
3 years ago
#2
(Original post by jasixa)
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.

(b) Find the probability that for a randomly chosen rod the measured length will be within 0.2 cm of the true length.

Two rods are chosen at random.
(c) Find the probability that for both rods the measured lengths will be within 0.2 cm of their true lengths.
What have you tried?
0
#3
(Original post by Kevin De Bruyne)
What have you tried?
i tried many times to solve this but I can't get the answer right
0
3 years ago
#4
(Original post by jasixa)
i tried many times to solve this but I can't get the answer right
What did you try? What was your most recent attempt at it?
0
#5
(Original post by Kevin De Bruyne)
What did you try? What was your most recent attempt at it?

For part a) because it said true length and it had no negative sign in front, I drew a uniform distribution between -0.5 and 0.5 and I did 0.2/1=0.2 but that's wrong answer.
0
3 years ago
#6
(Original post by jasixa)
For part a) because it said true length and it had no negative sign in front, I drew a uniform distribution between -0.5 and 0.5 and I did 0.2/1=0.2 but that's wrong answer.
Good start, right distribution.

Let's say a rod is truly 15.19999 cm and it says 15cm. Is it within 2cm of the true value?

Let's then say a rod is 14.80001 and it says 15cm. Is it within 2cm of the true value?
0
3 years ago
#7
Just imagine the distribution ranging from -0.5 cm to 0.5cm. Part b) asks for if it was within 0.2cm of the true value.

The mean of this distribution can be labelled as the "true value" i.e 0 because it is 0 it can't be in any way either below or above the true value, it must be the true value!

Thus if it is asking for 0.2cm WITHIN the true value this means 0.2 both below and above the true value.

i hope this has given enugh clues.

For part c) The probability you would have found would be for 1 of these rods, so using your knowledge of probabiltiy, what would it be for 2?
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