Students add and subtract with numbers expressed in scientific notation. They begin by studying expressions and determining the number of nonzero digits when evaluating each expression. This encourages students to make sense of how operations with scientific notation are alike and different. 

Next, students critique three different strategies for adding and subtracting numbers in scientific notation (MP3). Students see that two of the strategies—writing the expression in decimal notation first, and rewriting one of the expressions so that they are both a multiple of the same power of 10—can both be used to perform these types of calculations.

Students continue to make sense of addition and subtraction with scientific notation and interpreting their results in context when comparing the width of 5 planets side-by-side to the diameter of the sun (MP2).