My daughter has just started high school and has come home with this question, amongst others. "A large circular pane of glass has a perimeter of 219.8cm, calculate the area of the glass"? Now it's been 25 years since I needed to use pi(stop laughing at the back). To get the radius I need to divide the perimeter(circumference) by pi and then divide the diameter by 2, correct? Then calculate the area by using the pi x r2(pi x radius x radius) correct? I get an answer of- area = 3846.5. According to my daughters friends rather stuck up school teacher mother, it's wrong. Is it, I'd dearly love to tell her she was in fact wrong. Sorry for boring you's but it's bugging me.

If you know the circumference of a circle, the area inside it can be found using the formula where: Area = circumference squared/ 4x pi http://www.mathopenref.com/circlearea.html

The method's right but you must have typed it into the calculator wrong or something. Answer 2 is also slightly off (rounding errors? 3.14 used for pi?) Remember not to quote too many decimal places or significant figures!

3844.55 to 2dp Circumference is 2 x pi x r. r = 34.98225649 ^2 = 1223.758269 Area = pi x r^2 = 3844.549988

Perimeter = pi x D = 2 x pi x r > 219.8 = 2 x pi x r > r = 219.8 / (2 x pi) = 34.98cm > Area = pi x r x r = pi x 34.98 x 34.98 = 3844.5 sq cm

It's right. Then 3846.5. It depends on how many places you are taking pi too. I suggest you get her sorted.