For a normal distribution, approximately what percentage of values lie within 2 standard deviations of the mean?
From Paper 3: Pure and Statistics
148 marks
A spinner lands on red with probability 0.25. It is spun 15 times. X is the number of reds.
(a) State two assumptions needed to model X as B(15, 0.25).
(b) Find P(X = 4).
(c) Find P(X ≥ 3).
(d) Find the mean and variance of X.
From Paper 3: Pure and Statistics
159 marks
The lifetime, L hours, of a type of light bulb is modelled by L ~ N(800, 502).
(a) Find P(L > 900).
(b) Find P(750 < L < 880).
(c) The manufacturer changes the design. The mean stays at 800 hours but now only 5% of bulbs last less than 720 hours. Find the new standard deviation.
Score 0 / 18 · 0 of 3 marked
This paper is written by Plasmo in the style of the AQA A-Level Maths exam. It is not a past paper and is not produced or endorsed by the exam board.