Saxon Course 2: Lesson 3 (Slides)

Lesson 3

• Unknown Numbers in Addition, Subtraction, Multiplication, and Division

​Unknown Number in Addition Equations

• When we see variables (letters) in a math equation, that is an unknown number.

  Example: 2 + 3 = A 2 + b = 5 c + 3 = 5

• The first one we can solve by adding 2 + 3 to get 5. A = 5

• To find b, we will have to subtract. 5 - 2 = 3 so b = 3

• To find c, we will also have to subtract. 5 - 3 = 2 so c = 2

​Unknown Numbers in Subtraction Equations

• Example: a - 3 = 2 5 - x = 2 5 - 3 = m

• The first one we must add 3 + 2 = 5 to solve. a = 5

• To find x we will subtract 5 - 2 = 3. x = 3

• To find m we will also subtract 5 - 3 = 2. m = 2

• We can check our answer by plugging the unknown number in to see if the equation works!

  Let's do it for the first example problem! We start by plugging a = 5 in to get 5 - 3 = 2. Yes, it's correct!

​Unknown Numbers in Multiplication Equations

• Example: 3 x 2 = a 3b = 6 c x 2 = 6

a

• The first one we multiply to find a. 3 x 2 = 6 so a = 6.

• To find b we will divide 6/3 = 2. b = 2

• To find c we will also divide 6/2 = 3. c = 3

​Unknown Numbers in Division Equations

• Example: 24/3 = a 24/b = 8 c/3 = 8

• To solve the first one, we divide 24/3 = 8 so a = 8

• To find b we also divide 24/8 = 3 so b = 3

• To find c we multiply 8 x 3 = 24 so c = 24

• Don't forget to check your answers!

​Daily Challenge!
Create your own unknown number equations by choosing addition, subtraction, multiplication, or division.
(Pick one)
Give 3 examples and then solve them!

​Here's mine:
5 x 2 = A 10 x b = 100 c x 2 = 8
A = 10 b = 10 c = 4

​Still confused about the lesson?

​Here's the whole lesson on youtube: