00:01
We have been given a probability density function.
00:04
F of x is equal to 0 .04 for all x between 53 and 78.
00:13
So what kind of distribution are we looking at here? well we're looking at a uniform distribution.
00:20
So if i mark x and f of x on the axes, between 53 and 78, every possible outcome is equally likely to occur.
00:31
So it looks like a box.
00:33
Outside the interval it drops immediately to 0.
00:36
So f of x is 0 otherwise.
00:40
For part a, we want the proportion equivalent to the probability of a random test meeting this criteria, the proportion that require more than 70 seconds.
00:52
So i'll mark that on here.
00:56
So we're looking at this bit here.
00:58
Now this is a probability curve.
01:00
The area of the blue rectangle is 1.
01:02
And if i find the area of the red rectangle, i'll have my solution.
01:06
So i'm going to make a fraction comparing the size of these two rectangles.
01:10
So blue one is 1, or length times height.
01:13
The red is also length times height.
01:16
They have the same height here.
01:17
The height is actually 0 .04.
01:20
So all that is left is to compare the relative lengths of the intervals...