# The Circumference of a Circle #2

On the last circumference post, we were learning about circumference of a circle with the radius. In this post, we will be practicing more of that and something else also.

Radius: 1/4 of 16. Diameter: Unknown. Circumference: Unknown. — Once again, we use the formula (2-pi-r) to solve the equation. So since the radius is 1/4 of 16 (meaning that it is 4). This time, instead of using 22/7, we can use 3.14 (which is the same as 22/7), So we need to do 3.14 x (4×2). The reason I added (4×2) is because it has to be the diameter x pi, and since the diameter is x2 the radius, the diameter would be 8. So 3.14 x 8 = 25.12.

Question #1: If the radius of my circle is 54cm, what would my diameter be? Figuring this out will be very easy if you remember the formula for finding the diameter with the radius. All we basically have to do is multiply 54 by 2 (in other words, 54 x 2.) Which should give you 108cm.

Questions #2: I am (n). If the radius of a circle is (n), what is the radius when knowing that the circumference is 42cm? Now, in order to find this out, we first need to know the formula. The formula to find the radius with the circumference is (Circumference/pi). Note that the / means divide. Now since the circumference is 42cm and pi is 3.14, we have to divide that so it gives us 13.37…. But that’s not the end! We still have to get the square root of the (circumference / pi) , which gives us 3.65650106. This is how we find the radius of a circle when we have the circumference. (The reason of needing to get the square root of 13.37 is because when you do that, the circumference / pi gives you radius [squared], but it’s not the radius itself, so you got to find the square root of it in order to get the radius itself)

Questions #3: My circumference is 300cm and my radius is 1/5 of the circumference. What is the radius? This question doesn’t require knowing the skills of circumference in any way, all you need to know is what 1/5 of 300 is. The answer is 60cm.