Date | May 2017 | Marks available | 2 | Reference code | 17M.2.sl.TZ1.4 |
Level | SL only | Paper | 2 | Time zone | TZ1 |
Command term | Hence and Find | Question number | 4 | Adapted from | N/A |
Question
In a large university the probability that a student is left handed is 0.08. A sample of 150 students is randomly selected from the university. Let kk be the expected number of left-handed students in this sample.
Find kk.
Hence, find the probability that exactly kk students are left handed;
Hence, find the probability that fewer than kk students are left handed.
Markscheme
evidence of binomial distribution (may be seen in part (b)) (M1)
egnp, 150×0.08np, 150×0.08
k=12k=12 A1 N2
[2 marks]
P(X=12)=(15012)(0.08)12(0.92)138P(X=12)=(15012)(0.08)12(0.92)138 (A1)
0.119231
probability =0.119=0.119 A1 N2
[2 marks]
recognition that X⩽11 (M1)
0.456800
P(X<12)=0.457 A1 N2
[2 marks]