Is a mirror always a direct reflection of the real object?

What makes a virtual image of a real object?

The following table shows the number of units of product produced and sold by a company during six years.

What is the difference between the number of units produced in 2017 and the number of units sold in 2014? 

The following table shows the number of units of product produced and sold by a company during six years.

In which two years were the maximum units sold?

The following table shows the number of units of product produced and sold by a company during six years.

What is the percentage of the number of units produced in 2017 more than the number of units produced since 2012?

The following table shows the number of units of product produced and sold by a company during six years.

Find the ratio of the total number of units sold in 2013 and 2015 to the number of units sold in 2015 and 2016?

A class has 90 students, of which 60 percent are girls and the rest are boys. Boys' average score in English is 30 percent higher than girls. If the average score of all students in English is 56, then what is the average score of only girls in English?

If ( 2x – y): ( 5x+3y)=3 : 8 then ( x² + y²) : ( x² – y²)=?