Arithmetic Grade Four

Lesson Forty-two: Missing Numbers

Study the following problems. 

   __ + 7 = 14		4 + __ = 14		8 + __ = 14

  15 - __ = 10		10 - __ = 3		__ - 7 = 2
In each case we want to put a number in the blank space which will make the number sentence true. We want to complete the number sentence so that we wind up with a true statement.

So let's look at each number sentence from above and fill in the missing number. 


  __ + 7 = 14,  missing number = 7, 	7 + 7 = 14

  4 + __ = 14,  missing number = 10	4 + 10 = 14

  8 + __ = 14,  missing number = 6	8 + 6 = 14

  15 - __ = 10, missing number = 5	15 - 5 = 10

  10 - __ = 3,  missing number = 7	10 - 7 = 3

  __ - 7 = 2,   missing number = 9	9 - 7 = 2
You can write reverse problems by converting addition problems to subtraction problems and switching the numbers around in subtraction problems. 

   7 + 7 = 14  and  14 - 7 = 7

   15 - 5 = 10 and  15 - 10 = 5

   10 - 7 = 3  and  10 - 3 = 7
This may give you an idea of how you can discover the identity of missing numbers in problems like the ones shown above. 

  If you are given:		Convert it to:		Answer:

    12 - __ = 6			  12 - 6 = __		  6

    4 + __ = 9			  9 - 4 = __		  5

    __ + 3 = 7			  7 - 3 = __		  4

    __ - 5 = 4			  5 + 4 = __		  9
You get to try a few for yourself on the next page.

Continue to next page of lesson