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 Proportions Inverse proportion Inverse proportion is when one value increase as the other value decreases. Think of how long it would take 5 worker to build a buildind.  How long would it take if they had 5 workers helping them?  How long would it take if they had ten workers helping you?  The relation between the time it takes to build a building and the number of people working is an inverse proportion.  The more people you have, the less time it takes. If you double the number of workers, the time is halved. If you treble the number of workes, the time becomes to a third. The cross-multiplication method We are going to apply the same method that we used to solve direct proportions to inverse proportions, but with one additional step to the process: flip over the second column numbers to make it work. A farmer has enough cattle feed to feed 300 hens for 20 days. If he buys 100 more hens, how long would the same amount of feed feed the total hens? A group of pupils hire a bus, at a fixed price, to go on a field trip. Initially 32 pupils were due to go on the trip at a cost of 15 euros per head but on the day there were 24 students on the bus. What was the cost per head for them? Solution =