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Question:

What is the area of a circle with a radius of 9 in? (Use 3.14 for π)

A 254.34 in²
Explaination


Remember the formula for the area of a circle:
πr² = area
Or:
π × r × r = area
Which stands for:
π(pi = 3.14) × radius × radius
Step 1: Substitute Our Numbers Into the Equation
So let’s look at our equation:
π × r × r
The problem has told us to use 3.14 for π and we can see that our radius is 9 inches.
Now our equation looks like this:
3.14 × 9 in × 9 in
Step 2: Solve
Now that we have substituted in our numbers, we can solve it.
Remember, with decimals, we pretend as if the decimals are not there. We do not line up numbers by their decimal point.
1 3
3.14
× 9
2826
Since there are a total of 2 numbers to the right of the two decimal points in the problem, there will be 2 numbers that are behind the decimal in the product. Therefore, the decimal point goes between the number 8 and the second number 2.
28.26 in
Now we multiply the 28.26 and the 9. We do not line up numbers by their decimal point.
72 5
28.26
× 9
25434
Since there are a total of 2 numbers to the right of the two decimal points in the problem, there will be 2 numbers that are behind the decimal in the product. Therefore, the decimal point goes between the first number 4 and the 3.
254.34 in²
So, the area is 254.34 in²