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 by 1,000, each digit moves three places to the left. Eg, units become thousands. Note: units are often referred to as ones. For example, 34 has 3 tens and 4 units, or we could say 34 has 3 ...