A rate tells you how much of one thing goes with ONE of another: 12 litres per minute, $2.50 per litre, 45 pages per minute. Everything in this topic is a single relationship — total = rate × number of units — turned whichever way the question needs. If the total and the units are given, divide to get the rate. If the rate and the units are given, multiply to get the total. If the total and the rate are given, divide to find how many units. The one habit that makes all three easy is finding the amount for ONE unit first, which is the same move you already use for fractions of a set. Two rates in one question, like a tap filling while a leak drains, combine into a single net rate before anything else happens — and two prices can only be compared once both are the price for 1 kg.
Worked example
Problem A printer prints 480 pages in 8 minutes. At the same rate, how long will it take to print 1200 pages?