I recently discovered that the way that prices are shown on rate signs for motor vehicle fuel varies quite a bit. Some display the current price in dollars, some in cents and some, confusingly, show both dollars and cents. None of the signs that I found actually showed the units being displayed ($, ¢, L, gal., etc). I decided that it would be a good topic for a Which One Doesn't Belong discussion that would focus in on decimals, place value and fractions as well as currency and volume measurement.
Here are some suggestions why each image might not belong as well as some additional information for discussion:
Top Left: This is the only fuel price sign with both a decimal and a fraction. It is from a Costco in Oregon. The price is $2.29 and 9/10¢ per gallon. Both dollars and cents are used in this price. If you assumed that the entire price was listed in dollars, then $2.29 and $9/10 would actually give a price of $2.29 + $0.9 = $3.19.
Top Right: This is the only fuel price sign with just one decimal. It is from a Shell station in Halifax, NS and is in Canadian cents per litre. In Nova Scotia, the price often doesn't end with the standard 9/10¢ since the price is regulated by the Nova Scotia Utility and Review Board and only changes once per week.
Bottom Left: This is the only fuel price sign with two decimals. It is from an Atlantic Superstore gas station in Dartmouth, NS. Similar to the sign above it (top left), it displays a price of $1.00 and 0.5¢ per litre. While probably not confusing to the average motorist, I find the use of two decimals to be mathematically troubling. Why not just list the price as $1.005?
Bottom Right: This is the only fuel price sign with no decimals. It is from a 76 gas station in Oregon and is in US cents per gallon. It is interesting to note that Oregon and New Jersey are the only two US states with laws prohibiting self serve at gas stations. This sign mentions "Mini Serve" to note that an attendant operates the pumps but does not provide any of the other services you'd expect with full service.
Nova Scotia Mathematics Curriculum Outcomes
Grade 5 N09 - Students will be expected to relate decimals to fractions and fractions to decimals (to thousandths).
Grade 5 N10 - Students will be expected to compare and order decimals (to thousandths) by using benchmarks, place value, and equivalent decimals.
Grade 6 N01 - Students will be expected to demonstrate an understanding of place value for numbers greater than one million and less than one-thousandth.
Grade 7 N07 - Students will be expected to compare, order, and position positive fractions, positive decimals (to thousandths), and whole numbers by using benchmarks, place value, and equivalent fractions and/or decimals.