Find the area of a circle whose circumference measures 100 cm.

Question

Area (to the nearest square centimeter) = cm2

I plugged in everything C = 2 r
C=2x3.14x100= 628 <<< The computer said it was WRONG !
Then, I tried C= 2X3.14X50= 314 !!!

If I am wrong can you EXPLAIN to me what I am doing wrong.

Answer 1

C = 2πr
r = C/2π

area = πr^2 = π(C/2π)^2 = C^2/4π

so, area = 10000/4π = 2500/π = 796 cm^2