Question

Explain how an estimate helps you to place the decimal point when multiplying 3.9 & 5.3

Answer 1

-- Look at the two numbers.

-- Say to yourself: "Self !  3.9 is close to 4, and 5.3 is close to 5.
So the product is going to be close to  (4 x 5) = 20."

-- Then do the real  multiplication.

-- On your paper or your calculator, you see the digits  2 0 6 7 .

-- From your estimate (20), you know that it can't possibly be
2.067  or  206.7  or  2,067.  It must be  20.67 .