In a class of 78 students, 19 study Physics, 64 study Chemistry, and 5 study neither. How many students study both Physics and Chemistry?

If Person A can complete a task alone in 20 days, and Person B can complete the same task alone in 30 days, how many days will it take them to complete the task if they work together?

If Person A can complete a task alone in 5 days, and Person B can complete the same task alone in 20 days, how many days will it take them to complete the task if they work together?

A sum of Rs. 5500 is strictly divided among three individuals A, B, and C in the ratio 3:4:4. What is the exact monetary share of person B?

In a certain code, if '+' means 'multiplied by', '-' means 'divided by', 'x' means 'minus', and '/' means 'plus', what is the value of the following mathematical expression: 20 - 2 + 4 / 12 x 7 ?

In a certain code, if '+' means 'multiplied by', '-' means 'divided by', 'x' means 'minus', and '/' means 'plus', what is the value of the following mathematical expression: 24 - 3 + 5 / 11 x 10 ?

At a professional networking event, there are exactly 21 people present. If every person shakes hands with every other person exactly once, what is the total number of handshakes that occur?