Students add and subtract multi-digit whole numbers through commonly used large place values by aligning place values, regrouping across one or more zeros, and using place-value representations to explain and check the standard algorithms. They add and subtract decimals through hundredths, estimate differences using rounding or compatible numbers, and assess whether exact results are reasonable. They solve one-step addition problems involving whole numbers, decimals, and appropriately represented fractions, as well as multi-step addition and subtraction problems using equations, models, and contextual reasoning.