ALGEBRA: Open Sentence

LESSON 3

ALGEBRA: Use of Letters in Mathematics 3

OPEN SENTENCE

This is a mathematical statement in which numbers and boxes(SPACE) are used. The boxes(SPACE) represent the unknown quantities (amounts).

EXAMPLE 1

3 + [ ] = 10

This open sentence above means 3 plus an unknown number equals 10

Guess what the unknown number is. Yes? Good! You got it!

3 + 7 = 10

See?   The unknown number is 7.

EXAMPLE 2 

What number will make the open sentence below true?

[ ] - 2 = 5

SOLUTION

[ ] - 2 = 5

This open sentence means that when 2 is subtracted from an unknown number the result is 5. When 2 is subtracted from 7 the result is 5.

Therefore, the unknown number is 7!

7 – 2 = 5

EXAMPLE 3

What number will make the open sentence below true?

 4 + 2 = [ ]
                  

SOLUTION

4 + 2 = [ ] 

                  

This open sentence means that the result of 4 plus 2 is unknown. But 4 plus 2 is 6.

Therefore, the unknown result is 6!

4 + 2 = 6

PUSH IT IN!

Now, you know what an open sentence is.

But do you know how to determine the unknown in an open sentence?

Answer true or false to the following statements:

1. When 5 is added to 6 the result is 11.
2. 2 plus 7 is 10.
3. 8 minus 6 is 2.
4. When 3 is removed from 9 the answer is 6.
5. 4 plus 3 is 8.

The answer to the true/false statements above is given below. If you got all the answer correctly then you have mastered how to determine the unknown in an open sentence. Go to the ACTIVITY and have fun! If you got any of the answers wrong, send me a COMMENT and let’s discuss it.

Answer: TRUE, FALSE, TRUE, TRUE, FALSE.

ACTIVITY

In each open sentence below, find the number which makes it true.

1. 9 + 5 = [ ]     
2. [ ] = 6 +3
3. 7 - [ ] = 3
4. [ ] - 5 = 7
5. [ ] + 4 = 9

Post the solution as a COMMENT to this lesson. Include your name or nickname and email because every COMMENTS will be replied. I’m expecting your COMMENT.

 

Congratulation! You've completed this lesson. Now let's go to LESSON 4: TURNING OPEN SENTENCE INTO ALGEBRAIC SENTENCE.