Subtracting
Line up by place value and subtract from the right. When the top digit is smaller, borrow 1 from the next column over, which adds 10 to this one.
⁶⁹¹ 703 − 268 ───── 435
3 is less than 8, and the tens column has 0 to borrow from, so borrow from the hundreds: 7 becomes 6, the 0 becomes 10, then 9 after lending 1 to the ones, and the 3 becomes 13. Now 13 − 8 = 5, 9 − 6 = 3, and 6 − 2 = 4.
Counting up
Across zeros it is often easier to count up from the smaller number. For 1,000 − 368: 368 to 400 is 32, 400 to 1,000 is 600, so the answer is 632.
Check it: add the answer to the number you took away. 435 + 268 = 703.
AFOQT questions on this: Questions missed