Compound Rule of Three with Trick In this video I explain how to solve compound rule of three problems using a trick that will require you to ask questions to find out if the quantities are directly proportional or inversely proportional. This method is good mainly because it makes calculations easier and helps those students who have difficulty orienting the arrows. Compound Rule of Three 1. A brickyard produces 1470 bricks in 7 days, working 3 hours a day. How many bricks will it produce in 10 days, working 8 hours a day? 2. Eighty bricklayers build 32m of wall in 16 days. How many bricklayers will it take to build 16m of wall in 64 days? 3. A bus travels 2232km in 6 days, running 12 hours a day. How many kilometers will it travel in 10 days, running 14 hours a day? 4. In a factory, 12 workers working 8 hours a day can make 864 cardboard boxes. How many boxes will be made by 15 workers working 10 hours a day? 5. Twenty machines, working 16 hours a day, take 6 days to do a job. How many machines will be needed to perform the same job, if they work 20 hours a day, for 12 days? 6. In a textile industry, 8 tailors make 360 ​​shirts in 3 days. How many tailors are needed to make 1080 shirts in 12 days? 7. A cyclist travels 150 km in 4 days, cycling 3 hours a day. In how many days would he make a 400 km trip, cycling 4 hours a day? 8. In a boarding school, 35 students spend 15,400 reais on meals for 22 days. How much would 100 students spend on meals for 83 days in this boarding school? 9. 27.4 kg of wool were used to weave 24 m of fabric 60 cm wide. What is the length of the fabric that could be woven with 3.425 tons of wool to obtain a width of 90 cm? 10. 2/5 of a job was done in 10 days by 24 workers, who work 7 hours a day. In how many days can this job be finished, knowing that 4 workers were laid off and that they now work 6 hours a day? 11. The consumption of 12 identical light bulbs, lit for 5 hours a day, in 39 days, is 26 kilowatts. Keeping only 9 of these light bulbs lit for 4 hours a day, how much will be the consumption in 30 days? 12. If 15 kg of paper corresponds to 3,000 sheets of 20 cm wide by 30 cm long, how many sheets of 15 cm by 20 cm will correspond to 7 kg of paper? 13. 1064 kg of hay are needed to feed 14 horses for 12 days. How much hay would be needed to feed 6 horses for 60 days? 14. 30 workers spend 15 days of 8 hours to build 52 m of wall. How many days of 9 hours will 25 workers spend to build 39 m of the same wall? 15. 6 workers, in 15 days, did half of the job they were assigned. At the end of that time, 4 workers left the job. How long will it take for the remaining workers to finish the job? 16. A fleet of trucks traveled 3,000 km to transport goods, traveling at an average speed of 60 km per hour, and took 6 days. How many days would it take for this same fleet to travel 4,500 km at an average speed of 50 km per hour under the same conditions? 17. The production of 400 hectares where 50 men work supports 5 families. How many families could be supported, under the same conditions, with 600 hectares and 60 men working? 18. If 16 men spend 10 days assembling 32 machines, the number of days that 20 men would need to assemble 60 machines is: 19. A vehicle travels a certain distance at a constant speed for 3 hours. How long would it take for it to travel 2/3 of that distance at a constant speed that was 3/5 of the previous one? 20. A construction project was completed in 60 days using 5 bricklayers and 10 apprentices. Knowing that the work of two apprentices is equivalent to that of one bricklayer, how many days would it take to complete the same work if we had 6 bricklayers and 12 apprentices? Video link: • Rule of three composed with Macete