Define the term: True class limits

The final marks in mathematics of $30$ students are as follows:

$53, \mathrm{61,} 48, 60, 78, 68, \mathrm{55,} 100, \mathrm{67,} 90, 75, 88, 77, 37, 84, 58, \mathrm{60,} 48, 62, \mathrm{56,} 44, 58, 52, 64, 98, 59, 70, 39, 50, 60$

Arrange these marks in the ascending order, $30$ to $39$ in one group, and $40$ to $49$ in second group etc.

The final marks in mathematics of $30$ students are as follows:

$53,\mathrm{61,48},60,78,68,\mathrm{55,100},\mathrm{67,90},75,88,77,37,84,58,\mathrm{60,48},62,\mathrm{56,44},58,52,64,98,59,70,39,50,60$

What is the highest score?

The final marks in mathematics of $30$ students are as follows:

$53,\mathrm{61,48},60,78,68,\mathrm{55,100},\mathrm{67,90},75,88,77,37,84,58,\mathrm{60,48},62,\mathrm{56,44},58,52,64,98,59,70,39,50,60$

What is the lowest score?

The final marks in mathematics of $30$ students are as follows.

$53,\mathrm{61,48},60,78,68,\mathrm{55,100},\mathrm{67,90},75,88,77,37,84,58,\mathrm{60,48},62,\mathrm{56,44},58,52,64,98,59,70,39,50,60$

What is the range?

The final marks in mathematics of $30$ students are as follows:

$53,\mathrm{61,48},60,78,68,\mathrm{55,100},\mathrm{67,90},75,88,77,37,84,58,\mathrm{60,48},62,\mathrm{56,44},58,52,64,98,59,70,39,50,60$

If $40$ is the pass mark how many have failed?

The final marks in mathematics of $30$ students are as follows:

$53,\mathrm{61,48},60,78,68,\mathrm{55,100},\mathrm{67,90},75,88,77,37,84,58,\mathrm{60,48},62,\mathrm{56,44},58,52,64,98,59,70,39,50,60$

How many have scored $75$ or more?

The final marks in mathematics of $30$ students are as follows:

$53,\mathrm{61,48},60,78,68,\mathrm{55,100},\mathrm{67,90},75,88,77,37,84,58,\mathrm{60,48},62,\mathrm{56,44},58,52,64,98,59,70,39,50,60$

Which observations between $50$ and $60$ have not actually appeared?

The final marks in mathematics of $30$ students are as follows:

$53,\mathrm{61,48},60,78,68,\mathrm{55,100},\mathrm{67,90},75,88,77,37,84,58,\mathrm{60,48},62,\mathrm{56,44},58,52,64,98,59,70,39,50,60$

How many have scored less than $50 ?$