Skill 6E
Problem Solving: Missing Addends
Here, you can see how understanding related facts and number families can assist with figuring out missing addend word problems. These are certainly "tricky" problems to say the least. In the word problem below, you could say that 12 - 5 = 7 gives the correct answer (which it does), however, what we are supposed to do in these algebra type problems is to first write an equation that describes exactly what is described in the word problem. Therefore, if we do this we should write 5 + ____ = 12 which matches the order given in the word problem. Then, after looking at this we can say, to find the missing addend here we need to make another equation which is 12 - 5 = 7 Students should be discouraged from "jumping the gun" and learn how to write down the first step to get a clear visualization of the problem and only then move onto the next step to get the final answer. This will be very important to help with future more complex algebra related problems.

Read the word problem. Then answer the question that follows.

Victoria has 5 seashells.
A friend gave her more seashells.
She now has 12 seashells.

Which number sentence would you first use to find
how many seashells Victoria's friend gave her?
      A. 12 + = 17    
      B. 5 + = 12    
      C. 15 - = 10    
      D. 5 + = 7