Pi is 3.14, and is an irrational number, meaning that it does not end and has no repetition of numbers in a row.
The area of the circle is calculated by multiplying pi by the radius.
3.14 * 10 = 314.16.
To round it to the nearest tenth, you must know whether the second decimal number is greater or less than 5. If it is 5 or greater, you round the first decimal up 1. If it is 4 or less, then you just remove the second decimal and keep the first one.
In this case, the answer would be approximately 314.2 because 6 is greater than 5, so you round up the 1 to a 2.