Subtracting Friendly Numbers

by Grade 4

are numbers that have 9’s in the

Ones like 39 or 59

Tens like 199 or 399

Hundreds like 3999 or 6999

We can change numbers into

so that they are easier to subtract in our heads!

Follow this simple rule:

You can change numbers if they:

Are close to a ten, hundred or thousand

305297

305-6 =299 (a friendly number)

297-6 = to become 291

Now subtract

299291

8

-

-

202144

202 -3 =199 (a friendly number)144 -3 becomes 141

Now subtract

199141

58

509386

509 -10 = 499 (a friendly number)

386 -10 becomes 376

Now subtract

499376123

-

-

Friendly Subtraction can also have

NUMBERS WITH 0’S

As a Second number

such as 200, 50, 800Why?

They are easier to subtract!

That’s why!

482295

+ 5 = 487

+ 5 = 300

Now subtract

487300187

-

-

841303

- 3 = 838

- 3 = 300

Now subtract!

838300

38

-

-

5

831508

Subtract 8 = 823

Subtract 8 = 500

Now subtract!

823500323

-

-

2 01 2000 Minus 1 to become 1999

Minus 1 to become 200

Now subtract!

1999 200

1 799

-

-

805598

Add 2 to become 807

Add 2 to become 600

Now subtract!

807600

2 07

-

-

4000 Subtract 1to become 3999

Subtract 1 to become 2494

Now subtract!

2495

39992494

5051

-

-

The End – now do your own in your scribbler on the next slide! Check them when you’re done all of them.

Now do these on your own paper:

1. 800 - 599

2. 3000 - 213

3. 4876- 2999

4. 5226 - 3796

(799 - 598=201)

(2999 - 212=2787)

(4877 - 3000 =1877)

(5230 - 3800=1470)

Did you find the mistake?