Grade 1/2 Support Documents
Parents……
I wanted to provide you with the names of the Mental Math Strategies that we have learned so that you can talk to your child and practice them at home.
Zero Rule – Zero doesn’t change a thing, the number stays the same – this works for both addition and subtraction because zero is an empty set. Ex. 3+0=3, 0+7=7, 9-0=9
One More Rule – (addition) It’s just the next number! Ex. 7+1=8
One Less Rule – (subtraction) It’s just the number before! Ex. 6-1=5
Two More Rule – (addition) Skip count 2 more from the number, an even number that has 2 added to it will have an even answer; an odd number that has 2 added to it will have an odd answer. Ex. 6+2=8 (even) 11+2=13 (odd)
Two Less Rule – (subtraction) Skip count 2 back from the number, an even number that has 2 taken from it will have an even answer; an odd number that has 2 taken from it will have an odd answer. Ex. 14-2=12 (even) 9-2=7 (odd)
Turn Around Rule – (addition) If you know that 4+2=6 then 2+4=6
Counting On – (addition) Don’t count everything, don’t count it all, say the big number in your head and count on the small! Ex. 6+3=9 say 6 and count on the 3 – 6.. 7,8,9
Counting Back – (subtraction) Start at the big number and count back the small
Take it All Away Rule – any number minus itself is zero because you TAKE IT ALL AWAY! Ex. 8-8=0
Sums of Ten Rainbow – (also called Rainbow Buddies or Compatible Numbers) These are all the numbers that go together to make a 10 – 0,10 1,9 2,8 3,7 4,6 5,5 and of course the turn arounds that go along with them! SO… 0+10, 10+0, 1+9, 9+1, 2+8, 8+2, 3+7, 7+3, 4+6, 6+4, 5+5
Doubles – Your child will know the chant and the actions that go along with each of the Double Rhymes.
1+1 two is more fun
2+2 there are 4 of you
3+3 don’t you bug me! (a bug has six legs)
4+4 there’s a spider on my door (a spider has 8 legs)
5+5 ten fingers are alive
6+6 twelve eggs let’s mix
7+7 fourteen days in heaven
8+8 sixteen crayons are great
9+9 eighteen wheelers drive fine
10+10 twenty and let’s start again!
Using Doubles to Subtract – If we know that 4+4=8 THEN 8-4=4 (extending thinking to HALVES)
Near Doubles – If you know that 3+3=6 then we know 3+4=7 BECAUSE 4 is one more than 3 and 7 is one more than 6 (your child can explain 3+4 is the same as 3+3+1 (the 4 is broken down into 3+1)
Fact Families – 3+4=7, 4+3=7, 7-3=4, 7-4=3
Related Facts – ex. – The numbers 9,3,12 can make 9+3=12, 3+9=12, 12-9=3, 12-3=9. These related facts help kids use addition to subtract.
Making a Ten – When we add 9 to a number – ex. 6+9 – we can make 9 into 10 by taking 1 from the 6 (because 9+1=10) leaving 5 more to be added into the 10.
The same can be said if we are adding 8 to a number – ex. 4+8 – we can take 2 from the 4 (because 8+2=10) leaving 2 more to be added into the 10. Your child knows that adding into a 10 is easy because of the 0 in the ones place.
