A cylindrical can of soup has a diameter of 7.3 cm.

Question

What is the circumference of the lid, to the nearest tenth of a centimetre? 

 

2) how would you check your answer to the question above ^^ to see if your response is reasonable ? (Explain please, thank you a million) 

Answer 1

Two things to know:

1) circumference of a circle, c = 2πr

and

2) diameter, d = 2r

 

From this you can find that r= 3.65 cm and from there

c = 2(3.65)π = about 11.47cm

 

The best way to check your answer, beyond doing the math backwards, is to think about the reality of it.  If you had an answer of 1.14cm, you know that is way too small, and likewise if you had 114.7 centimeters, that is over 3 feet in length!  Common sense will help you get some guidance on that part.