There are many ways to do this, but the easiest way is using a calculator.

Or else you can multiply the two numbers together, just ignoring the decimal points for now.

You end up with the number 317492. But where do you put the decimal point in your final answer?

Just add together the total number of decimal places from the original numbers: 7.82 and 4.06. That is, the total number of digits which are to the right of the decimal points. The total here is 4. (The digits 8, 2, 0, and 6 are all to the right of the decimal points. That's a total of 4 digits.)

So in your final answer, just put 4 digits to the right of your decimal point.

In this case, it's 31.7492

If doing this sort of sum with a calculator, it's easy. If you want to do it longhand, you can draw a grid between the numbers, and multiply each one separately.

So you do 7 x 4 = 28, and 8 x 4 = 32, and 2 x 4 = 8, and put the numbers in as shown in the image.

Then you just add up along the diagonals, and you get the answer 31.7492. It's a great technique if you don't have a calculator with you

7.82 times 4.06 is equal to 31.7429

Multiply each number of 4.06 with each the number 7.82 and write down the result on top of each other. Put an additional cross mark below the rightmost digit with every row of numbers. Now add all the numbers considering the cross marks as zeros.

The result is 31.7429