Answer :

To Find the Fraction of the rectangle Arun painted blue,we can substract the fractions of green and red from the whole.

Arun painted:

5/8 of the rectangle green

1/4 of the rectangle red

since the whole rectangle is 1 ,we can substract the green and red parts from 1 to find the blue part

1-(5/8 + 1/4)

First we need to find a common denominator for the fractions,  the common denominator is 8,so we convert _1/4 a to 2/8:

     1 - ( 5/8+2/8)

so,    1- 7/8

Subtracting the fractions give us the blue part

1/8

so  ,Arun painted the 1/8 of the rectangle blue.