Kuala Lumpur Trial 2025 Add Maths Paper 1, Question 5
Solved on video in English · 4:25 video
The question
Diagram 2 shows the probability distribution of X. The discrete random variable X has a binomial probability distribution with n = 4, where n is the number of trials. Find the value of k.
A discrete random variable X has a binomial distribution, X ~ B(n, p), with a mean of 48 and a standard deviation of 4. Find the value of n and of p.
4:25Part (a)
Step 1
All the probabilities of a distribution add up to 1.
Why this step
The five crosses cover every possible value of X, so together they make certainty, which is probability 1. That single fact lets us find k.
3 more steps, each with the reason for it, in the full solution
Final answer
k = 1/3
Where students lose marks
Watch out: all probabilities add up to 1, so set the sum equal to 1 and take care adding 1/12 and 1/4.
Part (b)
3 more steps, each with the reason for it, in the full solution
Final answer
n = 72, p = 2/3
Where students lose marks
Watch out: npq is the variance, so square the standard deviation (4² = 16), and don't mix up p and q.
Watch every step of this question solved on video (4:25), with the reason behind each step and a box that checks your own answer.
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