A number is increased by 20% and then decreased by 20%, the final value of the number?

A) Does not change

B) Decreases by 2%

C) Increases by 4%

D) Decreases by 4%

 

Let the number be 100 %
It is given that first the number is increased by 20 %
So, 20 % of 100 % = (20/100) x (100/100)
                                     = 20/100
                                     = 20 %
So, increase in number = 100 % + 20 %
                                      = 120 %
Also given that the number is decreased by 20 %
Hence, 20 % of 120 % = (20/100) x (120/100)
                                     = 24/100
                                     = 24 %
So, decrease in number = 120 % – 24 %
                                       = 96 %

So number decreased = 100% – 96 % = 4 %

 

A cube has a volume of 8 cubic meters, If each side is doubled in length what will its new volume be in cubic meters?

A) 16

B) 32

C) 48

D) 64

We know that:

Volume of cube = a³

                        8  = a³

                        2³= a³

                ⇒     a= 2 m 

when side is doubled,

                        a = 4 m

so , new volume is:

                        V = 4³

                        V =64 m³