If the sum of the diameters of two circles is 30 cm and the difference of their radii is 5 cm, then the ratio of area of the smaller circle to that of the bigger circle is:
Answer & explanation
Correct answer: option 4
We have,
The sum of the diameters of two circles is 30 cm and the difference of their radii is 5 cm.
Let the radii of two circles = R and r
According to the question,
D + d = 30
So, R + r = 15
and R - r = 5
so, R = ( 15 + 5 ) /2 = 10
and r = 5
So, The ratio of area of smaller circle to the bigger circle = r2 : R2
= 52 : 102
= 25 : 100 = 1 : 4