Circumference!!!!!!HELPPPPPPPPPPLLLLLLLLZZZZZZZ!!!!!!!!!

[maths!]

help plz!!!!!!!

A circle has a circumference of 120cm. what is the radius of the circle?

show your working:


PLZ CAN SOME 1 HELP

 

[Unco]

What is the formula for circumference?

 

[maths!]

3.142*r*r

 

[Unco]

Good. So if our circumference is 120cm ... ???

 

[maths!]

i don't exactly know what to do. do i find the square root of it?

 

[Unco]

You have found the equation to be 120 = 3.142r^2.

Square rooting is the way to go, good job! <- bad me: thought you had divided first. This post it not clear.

 

[maths!]

thanks.i got the square root of 120 is 10.95445115. should i round up to 1 significant figure?

 

[Unco]

You have to divide by 3.142 first.

 

[maths!]

so i divide 120 by 3.142?

 

[Unco]

Yes.

 

[maths!]

i did 120 /3.142 and i got 38.19223425

 

[Unco]

Indeed. You had
120 = 3.142r^2

and you divided by 3.142 to get

120/3.142 = r^2

I think you know how to find r now.

 

[maths!]

do i square root the answer?

 

[Unco]

The square root of r^2 is r.

 

[maths!]

so do i square root the answer to 120/3.142?

 

[Unco]

*sigh*... yes.

 

[maths!]

do i round the answer 38.1922345 to 1 decimal place?

 

[Unco]

You were given two significant figures in the question (the 1 and 2 from 120*), so 2sf would be the way to go.

* This may have been rounded down from, say, 122 so we can only take 2 sf from it.

 

[maths!]

so would it become 38.19?

 

[Unco]

That's 2 decimal places (2dp). If you have not learned of significant figures yet, don't worry about it. FYI, here, 2sf would be equivalent to 0dp (because you would have just the 3 and 8 digits and no decimals). So 0 dp is good, but if that sounds strange to you 1dp is good also. 2dp is a bit too accurate for the numbers we based our calculations on.