Marks	No. of students
$1-20$	$8$
$21-40$	$12$
$41-50$	$15$
$51-60$	$20$
$61-70$	$13$
$71-80$	$17$
$81-90$	$5$

Number of students obtained marks between $41$ to $80$

Q.

Marks	No. of students
$1-20$	$8$
$21-40$	$12$
$41-50$	$15$
$51-60$	$20$
$61-70$	$13$
$71-80$	$17$
$81-90$	$5$

find probability that

Q.

Marks	No. of students
$1-20$	$8$
$21-40$	$12$
$41-50$	$15$
$51-60$	$20$
$61-70$	$13$
$71-80$	$17$
$81-90$	$5$

Write the probability of a student obtain less than $51$

Q. The marks obtained by 40 students of a class are given below: 80, 10, 30, 70, 60, 50, 50, 40, 40, 20, 40, 90, 50, 30, 70, 10, 60, 50, 20, 70, 70, 30, 80, 40, 20, 80, 90, 50, 80, 60, 70, 40, 50, 60, 90, 60, 40, 40, 60 and 60.
How many students obtained marks below 40

Q. Calculate the mean of the distribution given below using the short cut method.

Marks	$11-20$	$21-30$	$31-40$	$41-50$	$51-60$	$61-70$	$71-80$
No. of students	$2$	$6$	$10$	$12$	$9$	$7$	$4$

Q. The marks obtained by 40 students of a class are given below: 80, 10, 30, 70, 60, 50, 50, 40, 40, 20, 40, 90, 50, 30, 70, 10, 60, 50, 20, 70, 70, 30, 80, 40, 20, 80, 90, 50, 80, 60, 70, 40, 50, 60, 90, 60, 40, 40, 60 and 60.
Find how many students have marks equal to or more than 70?