The diameter of the circle was increased by 10%. How many percent were increased in this case:

The diameter of the circle was increased by 10%. How many percent were increased in this case: 1) the circumference; 2) the area of a circle bounded by a given circle?

1) D = L / pi, where D is the diameter of the circle, L is the circumference, pi is the number of pi, equal to approximately 3.14.
If the diameter is increased by 10%, we get the equation:
1.1 * D = L / pi; L = 1.1 * D * pi.
Answer: The circumference will also increase by 10%.
2) S = 1/4 * pi * D ^ 2, where S is the area of a circle.
If the diameter is increased by 10%, we get the equation:
S = 1/4 * pi * (1.1 * D) ^ 2 = 1/4 * pi * 1.1 * D * 1.1 * D = 1/4 * pi * 1.21 * D ^ 2.
Answer: The area of the circle will increase by 21%.