Question

if 75% of the students of a class of 48 students are exceptionally good in maths what is the probability that a student selected at random is a) weak in maths
b)good in maths

Answer 1

a) probability weak in maths=
$\frac{12}{48} = \frac{1}{4}$
b)probability good in maths =
$= \frac{36}{48} = \frac{3}{4}$

Answer 2

given 75 '/:=48
48/75=o.64
0.64×100=100
total number of students in class be 64 in this 25 are weak =0.64×25=16
prob of weak in mat be =16/64=1/4
prob of good in mat be 48/64= 3/4
let prob of weak be p =1/4
let total prob =prob of weak+prob of good
prob of total for any be 1
1=1/4+prob of good
prob of good be q =1-p=1-1/4=3/4