Rachel picked 28 apples from her tree. If the tree had 49 apples initially. How many apples are still there on the tree?
1. Rachel picked 28 apples from her tree. 
2. If the tree had 49 apples initially, 
3. How many apples are still there on the tree? 

We are looking for the number of apples that are still on the tree. This is the number of apples that Rachel did NOT pick. 

We can solve this problem using a number sentence. 

49 - 28 = 

21