While solving various Entrance tests, you may come across questions regarding calculation of number of various geometrical figures, lets learn some shortcuts and tricks to calculate the number of such geometrical figures in fraction of seconds.
Here we will learn tips and shortcuts to calculate the number of Rectangles

Start with the number of rows in the grid, and multiply it by the number of columns in the grid. This will give you the total number of unit squares in the grid.

Take the square root of the result from step 1. This will give you the length of one side of the largest square that can be formed by the unit squares in the grid.

Multiply the length of one side of the largest square by itself. This will give you the number of unit squares in the largest square.

Subtract the number of unit squares in the largest square from the total number of unit squares in the grid. This will give you the number of unit squares that are not part of the largest square.

Take the square root of the number of unit squares that are not part of the largest square. This will give you the length of one side of the secondlargest square that can be formed by the remaining unit squares in the grid.

Multiply the length of one side of the secondlargest square by itself. This will give you the number of unit squares in the secondlargest square.

Repeat steps 5 and 6 for each of the remaining squares in the grid, until you have counted all of the unit squares.

Add up the number of unit squares in each of the squares you counted in steps 57. This will give you the total number of rectangles in the grid.