SPM 2018 Add Maths Paper 2, Question 9
Solved on video in English and Bahasa Melayu · 10 marks · 6:12 video
The question
A study shows that the credit card balance of the customers is normally distributed as shown in Diagram 6. (a)(i) Find the standard deviation. (ii) If 30 customers are chosen at random, find the number of customers who have a credit card balance between RM1 800 and RM3 000. (b) It is found that 25% of the customers have a credit card balance less than RM y. Find the value of y.
[10 marks]
6:12Step 1
The 50% region lies to the left of x = 2870, so this vertical line is the mean: μ = RM2870.
Why this step
A normal curve is symmetric, so only the mean splits the area 50% and 50%. That is how we spot the mean from the diagram.
8 more steps, each with the reason for it, in the full solution
Final answer
σ = 900; 13 customers; y ≈ RM2263
Where students lose marks
Watch out: keep signs straight. Z for 1800 is negative, and y lies below the mean, so z = −0.6745.
Watch every step of this question solved on video (6:12), with the reason behind each step and a box that checks your own answer.
No card. Every past-year question on video, in English and BM.
Questions are re-typeset by Eduly for study and commentary. Eduly is not affiliated with Lembaga Peperiksaan Malaysia or the Ministry of Education.