## Friday, August 29, 2008

### Rates and Ratios

Rates and ratios is one of those topics that I always have troubles teaching - especially to weak classes with poor fractions.

It is a large topic and covers many areas:
• parts of a whole (eg. 2 boys: 3 girls)
• parts of the whole (2 boys: 5 students total)
• scaling factors (1:100)
• equivalent ratios (2:4 as 1:2)
• conversion of fractions to ratios (2 blue:3 green = 2/5 blue)
• comparing unit values (1.25L of Coke @ \$1.15 & 2L of Coke @ 2.35)
• unit conversions (dilute 1mL : 2L -> how much for 5L)

I don't think teaching this topic to 7's or 10's that I've established a sequence that enables students to grasp the concept easily. A few successful strategies have been corners and calculating ratios of m&m's and smarties. Mapping activities have been good (find ten cities in ten different countries and find the actual distance travelled) for large unit conversion activities. The grid activity where students grid a picture and then construct an enlarged grid and redraw the picture inside also works well.

I think next year when the topic is introduced I'll define ratios as a way of 'describing a groups of things' and then launch into proportions.

This is definately one that needs more attention on the programme and the sourcing of more resources for next year.