Students add and subtract whole numbers within 20 by modeling joining, separating, comparing, and finding missing parts, using counting on or back, making ten, doubles, near doubles, number bonds, and fact families. They interpret and write addition and subtraction equations, including the plus, minus, and equals signs, and solve one- and two-step word problems with unknowns in any position. They also add one-digit numbers to multiples of ten and add or subtract two-digit numbers without regrouping, using place-value reasoning within 100.