How do you know that 10 times 67.3 is 673 but not 6730?

Answer 1

When multiplying by 10 you shift the decimal point one digit to the right.

Therefore 10 x 67.30 becomes 673.0 (or 673).

(100 x 67.30 becomes 6730 because you would have shifted the decimal point 2 digits to the right).