Multiplication and Division
In third grade we have been learning strategies to solve multiplication and division problems. Knowing the facts is important to fluency! To have a strategy will allow students to solve quickly and efficiently.
We began with X 5's because students have been counting by 5's since kindergarten or first grade. At this point, they are good at skip counting by 5's and do so almost from rote memory. The kiddos can "anchor" their thinking to different x 5 they know to help figure out an unknown x 5. For instance, if I don't know what 7 X 5= I can think about 5 X 5 =25 and count up from there by 5's.
Next, we learned our X 10's Again students have been skip counting tens since K/1st grade and at this point have done plenty of work with place value. Students simply think of 4 X 10 = as 4 sticks of ten, giving them 40!
Although counting by 2's seems logical here, the most efficient way to approach X 2 is to think of DOUBLES! Multiplicaiton is repeated addition, therefore thinking of the addition doubles facts is far faster than count by's.
9 X 2= 2,4,6,8,10,12,14,16,18 OR 9 + 9=18. Again, the goal with multiplication and division facts is fluency! Quick and efficient!
Once we are good at our X 2 (doubles), our 3's come pretty easily. For example, 3 X 6 can be thought of at 6 + 6 is 12 +one more group of 6 = 18! This strategy is referred to as Doubles plus another set. It is important the child be able to think of the double fact mentally.
when the students explored multiplying with 4, they realized when they laid out their problem using numbers or an array that this strategy was a DOUBLE DOUBLE. Watch the video below to see what that means.
It's tempting to teach a "trick" with your fingers for this difficult multiplication and division number! The number is big, it isn't easy to skip count using 9's...what will we do? We will use our X 10 to help us!