Answer:
The decimal point should be moved to the right four times
Explanation:
For quick multiplication with 10, 100s or 1000s, the decimal point in the original number is moved to the right the same number of times as the number of Zeros in the multiplying factor.
In this example, to calculate 38.57 × 10,000, the multiplying factor is 10,000 with 4 zeroes, hence the decimal point is moved to the right 4 times as shown;
original decimal 38.57
1st move: 385.7
2nd move: 3857.0 (Note that for every move beyond the last digit in the number, a zero is used to show every further point moved)
3rd move: 38570.0
4th move: 385700.0
hence 38.57 × 10,000 = 385700.0 or simply 385700.
Note also that for divisions, the same rule holds but instead of moving the decimal point to the right, it is moved to the left.