19 is only 1 away from 20, so you prefer to start by multiplying 20 times 5, which equals 100. Then we need to take away a squadron of 5, because there are actually only 19 squadrons, not 20. 100 take ...

To multiply decimals by 10, 100, and 1000, use place value labels. Write the digits of the decimal using place value labels. Start with the first non-zero digit. To multiply by 10 move each digit one ...

Now that we've learned the basics of lightning fast mental addition, mental subtraction, and mental multiplication, it's time to turn our attention to a few tips that will help you take your skills to ...