5. If the radius of a circle is increased by 20% then the area is increased by:

A. 44%

B. 120%

C. 144%

D. 40%

None of the above

A. 44 %

Step-by-step explanation:

Suppose Area of a circle is A=πr^2 (1)

When radius increase by 20%

r'=r + 20/100 r = 1.2 r

Now area

Area = πr'^2

= π (1.2 r) ^2

= 1.44πr^2 (2)

Difference between the area (1) and (2)

=1.44πr^2-πr^2

=.44πr^2

Taking percentage

=.44πr^2*100/πr^2

=44%

Hence 44% is answer.

Example:

radius of the circle (before) = 10cm

radius of circle (after)

100% = 10

120% = 12

area of circle before = pi x 10 square = 314.15

area of circle after = pi x 12 square = 452.38

percentage increased

= area of circle (after) - area of circle (before) divides by area of circle (before) x 100%

= 44%

Answer : A

(Sorry if it's wrong, I tried my best)