Question

How estimation helps you to place the decimal point when multiplying 3.9x5.3

Answer 1

3.9 is nearly 4 and 5.3 is just over 5 so the answer will be in the region of 15 or thinking about the decimal point there will be a tens and unit answer followed by a decimal point

Answer 2

3.9 can be rounded to 4.
5.3 can be rounded to 5.

4 x 5 = 20

That tells you that 3.9 x 5.3 has a digit in the tens place.

Then you can proceed to multiply 39 and 53, which equals 2067.
(Note: I removed the decimals on purpose)

Now we know that in 2067, the 2 should be in the tens place. That means 0 is in the ones place and that 6 is in the tenths place. That leaves 7 to be in the hundreths place.

Therefore, 3.9 x 5.3 = 20.67