⁦Adding and subtracting a sum⁩

⁦In Ukrainian Grade 2 children learn expressions with⁩ brackets. To ⁦add a sum to a number⁩, ⁦add one addend and then the other⁩: ⁦7 + (3 + 2) = (7 + 3) + 2 = 10 + 2 = 12⁩. ⁦Choose convenient addends so the first number reaches a ten⁩.

To ⁦subtract a sum from a number⁩, ⁦subtract the addends one after the other⁩: ⁦11 − (1 + 5) = (11 − 1) − 5 = 5⁩. To ⁦subtract a number from a sum⁩, ⁦subtract it from one addend and add the other⁩: ⁦(10 + 6) − 8 = (10 − 8) + 6 = 8⁩.

⁦The book writes the rules with letters⁩: ⁦a + (b + c) = (a + b) + c; a − (b + c) = (a − b) − c; (a + b) − c = (a − c) + b⁩. ⁦The associative law of addition is (a + b) + c = a + (b + c)⁩.