Multiplying mixed numbers – Grade 4

[Duane]

Bill, in a previous thread (http://commoncoretools.me/forums/topic/mixed-numbers-in-grades-4-and-5/) we discussed how the word “fraction” in Grade 4 can include mixed numbers. This use of “fraction” meant that the example on page 8 of the NF Progressions of 43 x (2 and 3/4) was acceptable for 4.NF.4.

Looking at the example once again, to get a product of 118 and 1/4 is quite an involved process. The method shown involves converting a mixed number to a common fraction, multiplying two 2-digit numbers (43 x 11), then dividing a 3-digit number by a 1-digit number (473 ÷ 4). While these individual steps are within the scope of the Grade 4 standards it seems a little too ambitious to roll them into one problem.

The Grade 5 standard 5.NF.6, where mixed numbers are explicitly mentioned, seems much better placed for this type of problem – that is, after students have had more practice with each individual step involved in the whole process. Is it really the case that mixed numbers have to be multiplied by whole numbers in Grade 4, or is it an optional extra?

[Bill McCallum]

Duane, I think there’s some room for maneuver exactly where this type of problem is introduced in the progression from 4.NF.3.c, which makes clear that mixed numbers are included in fractions, and 5.NF.6. And the particular task you cite might well be better aligned with 5.NF.6.

[Author]

Posts