The new forums will be named Coin Return (based on the most recent vote)! You can check on the status and timeline of the transition to the new forums here.
The Guiding Principles and New Rules document is now in effect.
2 Math Questions - Area of Circles
Underdog
Registered User regular
Registered User regular
I'm filling in the homework for my class and I want to make sure I'm doing these two questions correctly.
1. The diameter of a circle is 10 cm. Find the remainin area if a frame of 2cm is to be cut off from the original circle.
Area would have been Pi x 5^2 but when you cut off 2cm for the frame, then the radius is shortened to 3. So I went with:
3^2 x 3.14 = 28.26
2. A circular picture of circumference 88 cm is mounted on a circular cardboard, leaving a margin of 7 cm all round. Find the area of the margin. Use 22/7 as Pi.
So the radius of picture is 88 / 22/7 = 14.
The radius of the whole cardboard then is 14 + 7 = 21.
So the area of the margin is:
21^2 x 22/7 - 14^2 x 22/7 = 770
Thanks!
1. The diameter of a circle is 10 cm. Find the remainin area if a frame of 2cm is to be cut off from the original circle.
Area would have been Pi x 5^2 but when you cut off 2cm for the frame, then the radius is shortened to 3. So I went with:
3^2 x 3.14 = 28.26
2. A circular picture of circumference 88 cm is mounted on a circular cardboard, leaving a margin of 7 cm all round. Find the area of the margin. Use 22/7 as Pi.
So the radius of picture is 88 / 22/7 = 14.
The radius of the whole cardboard then is 14 + 7 = 21.
So the area of the margin is:
21^2 x 22/7 - 14^2 x 22/7 = 770
Thanks!
Underdog on
0
Posts
the second one 14 cm is the diameter not the radius.
14^2 x 22/7 - 7^2 x 22/7 = 462
I think your answer was right the first time, you just wrote this down wrong. It should be
radius of picture = 88 / 22/7 / 2 = 14.
21^2 x 22/7 - 14^2 x 22/7 = 770
0431-6094-6446-7088