How to Figure out circumference with given radius

Here Mr Misonet tries to teach to compute circumference of a circle when radius is given. First he convince you the formula. The circumference of a circle is proportionately equals to "pie" times of its diameter,where the value of "pie" is equal to 3.14 and diameter is equal to two times radius. Then he puts the value of the diameter of the given circle and calculate the value of the circumference and also make you understand how to multiply the numbers with decimals. And lastly he makes your concept clearer that circumference of a circle is approximately three times more than its diameter.