Gas Cost

I’m heading to OAME in London, and my grade 9s helped me determine how much I will spend on gas for the trip. We looked up on a map that it will be 440km from Kingston to London. Gas today costs $1.64/L and then we needed to find how much gas it takes to drive my car for a certain distance, the fuel efficiency. Looking up online we saw that my car has an efficiency of 7.5L/100km.

Groups used different strategies to do calculations, and it’s interesting to see how they approached the task.

Some started by multiplying 7.5×4 which is 30, which makes sense because it’s 7.5L per 100km and there are 4 groups of 100km in 440km (the total distance). Next we need to multiply 7.5 by 0.4 since there’s a total of 4.4 groups of 100 km in 440km. To do this multiplication some groups divided 7.5 by 10 which is 0.75 to find out the value for 1 tenth and then multiplied by 4 to get the value for 4 tenths (which is 3). The final value for 7.5×4.4 is then 33. All of this can be done without a calculator. This tells us how many litres are needed for a one way trip. Since we’re going both ways we need twice that, so 66L. Next we multiply by the price per L.

Other groups started multiplying 1.64 by 7.5 which gives the price for the gas that will take you 100km. Then you multiply by 4.4 to get the price for 440km, then double it for the entire journey.

Some groups wrote it all down like fractions and proportions, and others wrote out their steps one at a time.

I’m glad to see a variety of strategies. Students are using methods that make sense to them, not just memorizing one way to solve a problem. I’m glad to help them develop a more deep connection and understanding of their numeracy skills.