In each of the statements above, there is a missing number called unknown represented by.[] They are called open sentences.

An open sentence is a mathematical statement that involves equality signs and a missing

quantity represented by[] that the four arithmetic operations of addition, subtraction,

multiplication and division can be applied to solve.

Open sentences can either be true or false depending on the value [].

Exercise

A. Write True (T) or False (F) for each of the following closed number sentences.

1. 15 + 16 = 31  2. 54 + 4 = 68   3. 18 + 10 = 38   4. 51 + 47 = 98

5. 29 + 60 = 82  6. 42 + 54 = 84   7. 55 − 23 = 33  8. 54 − 11 = 43

9. 64 − 43 = 21  10. 98 − 45 = 53