These best buy questions were very in vogue when I started teaching every exam paper without fail had a best value question. I can still picture the washing powder boxes with their greyed out images those of you have been around awhile will still see them too. As I may have mentioned before one of my roles was to achieve 100% pass rate in a school that I taught in. As the best buy questions tended to be on the calculator paper we often felt these were easy marks that our lower sets could achieve.
It was my job to come up with a department wide approach for tackling best buy questions for those students lower set or higher set who just didn't get it. I cannot tell you how many times in my experience of working in schools marking mocks papers I have seen the division the wrong way round!
Picture the morning of the exam. The free snacks or breakfast flowing and the whole of year 11 are looking at me for last minute tips. I was the lead presenter as the rest of the department floated around helping the panickers. I had been looking into all sorts of ways to solve the department wide problem of answering best buy questions so this wasn’t entirely out of the blue but I hadn’t firmed up my plans at this point. By opening my mouth I suddenly did firm up the department wide approach much to the shock of the head of department who was watching on!
Price
Quantity
Yes there are best value questions where multiplying quantities up would give a more sensible answer but this became the approach for calculator best value questions. This may lead to fractional pence answers but it does give two prices that can be compared and a decision made on which is best value. I tell my learners that if they have their own way then they should use that but this may inspire some to tackle questions that they previously avoided. It also provides a nice opportunity to revisit rounding and significant figures. as I've said before rounding and significant figures is something that needs constant reminding and reinforcing and is always in my retrieval practice grids.
In the department I was in we began to look at other opportunities for marks for our lower sets. We looked at two way tables. We found the learners enjoyed completing the tables but struggled to pull out the final fraction.
I began by asking my students how they would work it out. The main question I was asked is “how do you know which number you want?” This was evident in their working out. Nearly all of the students had 100 as their denominator with a variety of 35 or 60 as the numerator. Keeping things as simple as possible I used the language of the students. I trialled what you get as a fraction of what you want. So in this example we want females and we get gym females.
This not only works for two way tables but any time a fraction from probability is required.
What is the fraction of red marbles in the bag that has 4 green and 6 red? 6/10. You want marbles, you get red. It’s quite simple and really helped us crack the using the wrong denominator in the two way tables.
