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 ...

What are positive and negative numbers? Any number above zero is a positive number. Positive numbers are written with no sign or a '\({+}\)' sign in front of them and they are counted up from zero to ...