Question

Marks	Number of Students
$0-20$	$7$
$20-30$	$10$
$30-40$	$10$
$40-50$	$20$
$50-60$	$20$
$60-70$	$15$
$70-$ Above	$8$
Total	$90$

A teacher wanted to analyze the performance of two sections of students in a mathematics test of 100 marks. Looking at their performance, she found that a few students got, under 20 marks and a few got 70 marks or above. So she decided to group them into intervals of varying sizes as follows: $0-20,20-30....,60-70,70-100$ Then she formed the following table.
(i) Find the probability that a student obtained less than $20$% in the mathematics test.
(ii) Find the probability that a student obtained marks $60$ or above.

Answer 1

Total students $=90$

(i) Number of students getting less than $20\%$ marks in the test $=7$
$P=\frac{7}{90}$

(ii) Number of students obtaining marks $60$ or above $=15+8=23$
$P=\frac{23}{90}$