In this lesson, students will add decimals. Understand that in order to add quantities, they must have the same unit (which in the case of decimals, are their place values). Add like units with decimals using an area model or the standard algorithm, aligning place values correctly (which results in the decimal points being aligned). Estimate sums of decimals. Understand that the commutative and associative properties still hold with decimal addition. Solve one-step word problems involving the addition of two decimals.