The US measurements is not a thing to get bogged down on. You'll move on soon.ChristyH wrote:My dd who is 11 and in 3B is struggling with gals, pts, and qts. addition and subtraction. I generally break these problems down to the lowest part and then subtract and then divide back up to whatever is asked for. This seems like the long way around for these answers and since they give you no room to write I am wondering if these are suppose to be done mentally. Any suggestions?
In 3B with the gallons, pints, and other US measurement we write it down on dry erase board if needed. I even have a hard time doing that in my head when I am cooking, so I don't care if my kids have to write it down to see it. It's a lot to track.
Typically my 10 y.o will do that along the lines of regrouping:
2 pints 1 cup
minus 2 cups
gets changed along the same lines of thinking of a subtraction problem of 21 - 2. it becomes "ten & 11" minus 2.
except that US measurements are not in groups of tens, which makes it rough to think mentally about. So, if they can't do it mentally, it's ok in my book. We use Pints and Cups as our place value grouping in the problem. (or as my dh likes to confuse me once in a while.... wow! you mean you're introducing math in things like base 16 (ounces to cup) and base 3 (cups to pints?) Don't make it mental math requirement right now for that, ok? thank you honey.)
so it is converted along the idea of basic grouping:
1 pint 3 cups (this is the same as 2 pt 1 cup, right? just like 21 is ten plus eleven when regroup)
minus 2 cups
1 pint 1 cup.
sometimes we've practiced it as
2 pt 1 c
- 2 cu
4 plus 1 cup, 5 cups
- 2 cups
equals 3 cups which is 1 pint 1 cup.
but that seems harder to my child. I don't know why yet. But she prefers to do it the stack it method. so I'm ok.
Yes, I can do it mentally, but I don't have the expectation that my elementary child HAS to do it mentally right now in3B or even at the stove when it really counts. Just like any other mental math in Singapore, we write down what we did to lock it in our brains, talk through the problem out loud for the process. write down and go longer if needed.
Find bottles and jugs around the house to use to help cement the amounts and all of that. We have measuring cups, drink bottles, milk jugs, etc. let them fill up the containers and look for those "skip's by 2's"