Question : In a class, the average height of all students is $a$ cm. Among them, the average height of 10 students is $b$ cm, and the average height of the remaining students is $c$ cm. Find the number of students in the class. (Here $a>c$ and $b>c$)

Option 1: $\frac{\left ( a\left ( b-c \right ) \right )}{\left ( a-c \right )}$

Option 2: $\frac{\left ( b-c \right )}{\left ( a-c \right )}$

Option 3: $\frac{\left ( b-c \right )}{10\left ( a-c \right )}$

Option 4: $\frac{10\left ( b-c \right )}{\left ( a-c \right )}$

Question : Directions: Select the set in which the numbers are related in the same way as the numbers of the following sets.
(NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into their constituent digits. E.g. 13 – operations on 13 such as adding/subtracting/multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is NOT allowed.)
$\left[\left(\frac{7}{9}\right),\left(\frac{31}{39}\right)\right];\left[\left(\frac{3}{5}\right),\left(\frac{15}{23}\right)\right]$

Option 1: $\left[\left(\frac{11}{13}\right),\left(\frac{47}{55}\right)\right]$

Option 2: $\left[\left(\frac{9}{13}\right),\left(\frac{37}{55}\right)\right]$

Option 3: $\left[\left(\frac{9}{11}\right),\left(\frac{32}{37}\right)\right]$

Option 4: $\left[\left(\frac{17}{19}\right),\left(\frac{36}{77}\right)\right]$