In third grade math, a number sentence is used to introduce simple mathematical statements to children. Number sentences can also include a less than or greater than sign in addition to other symbols.
Number sentences do not necessarily have to be true. Some teachers show number sentences that are not true to help teach children about math. Some number sentences have question marks in the middle as a way to introduce algebra. For example, “If trying to calculate 10 + ? =15, what is the missing number?” Number sentences also use the greater than or equal to sign or the less than or equal to sign. The not equal to sign appears in number sentences as well. These sentences can have two sides to them with an equal sign in the middle. An example is “5 +2= 6 +1” This is part of the reason why number sentences are not equations and are instead simply there to introduce third graders to more complicated and formal concepts they need to know later in school.
Number sentences also often introduce children to ideas like order of operations, variables and parentheses. It is a natural progression to go from question marks in number sentences to variables like “X” in algebra.