2-4

1st

• Pick a number for the math expression
• Then add to it to make it friendly
• 26 - 18 =

Did you pick the number 18?
Let's add 2 + 18
That changes 18 to 20
That is a friendly number

Friendly numbers are usually multiples of 5 and 10.

So now that we added 2 to 18 and made it 20.
We need to add 2 to the other number in the math expression.
26 + 2 = 28

Let's Review the steps so far

• 26 - 18 =
• add 2 to 18 = 20
• add 2 to 26 = 28

Now the new equation is 28 - 20 =
Can you subtract that in your head?

Yes

So, to subtract numbers in your head first you need to

• Pick a number that you want to change into a friendly number.
• Add to that number to make it friendly
• Add the same amount to the other number in the equation
• Last subtract the new numbers in your head.

Let's try it!

34 - 19 =

34 - 19 =
19 + 1 = 20
34 + 1 = 35

35 - 20 =

Great Job!