Uniform Distribution - Solving Qc and Qd for Screen Placement | Math Homework

[jsmith613]

Homework Statement

http://www.xtremepapers.com/Edexcel/Advanced%20Level/Mathematics/Subject%20Sorted/S2/Solomon/Solomon%20B.pdf

Questions 3c and 3d

Homework Equations

The Attempt at a Solution

ok so for Qc) it must be between 6 and 10 cm from the bottom and 8 and 12 cm from the left

d) it must be within a square 2 cm all the way around the outer full screen

But I don't see how to calculate the answers - there are an infinite number of solutions

 

[Joffan]

Prefacing everything with "Assuming X and Y are independent"... and for extra deviousness, "and that the screen is 20cm x 16cm".

For c), it occupies 1/5 of the horizontal distance and 1/4 of the vertical distance.

For d), take a clue from above and work out the probability of a dot appearing in any 1 cm² of the screen.

 

[jsmith613]

ok so c) 1/20

d) any 1 cm² = 1/320
(16*20)-(16*12) = 128
1/320 * 128 = 2/5

is that right?

 

[Joffan]

apart from needing some explanatory text, looks ok

 

[jsmith613]

what explanatory text

 

[Joffan]

To quote the front page of the paper:

Advice to Candidates
You must show sufficient working to make your methods clear to an examiner.
Answers without working will gain no credit.

 

[jsmith613]

me sad
but thanks for that!