Four-digit numbers times and divided by two digits

Four digits times two digits: split the two-digit number into tens and ones, multiply twice, then add: 2345 × 36 = 2345 × 30 + 2345 × 6 = 70350 + 14070 = 84420. Written in columns it is the same; the tens row is times 30, so it moves one place left (ending in 0). Four digits divided by two digits: see whether the first two digits are big enough to divide, and if not, use the first three; round the divisor to tens to try a digit. 7344 ÷ 24: 73 ÷ 24, try 3, 24 × 3 = 72, 1 left; bring down the 4, 14 is too small for 24, so write 0; bring down the next 4, 144 ÷ 24 = 6. The quotient is 306. A remainder can be written as a fraction too, the remainder over the divisor: 7349 ÷ 24 = 306 … 5, which is 306 524. Another way: estimate the size first (2000 × 40 = 80000), then check with the inverse: 306 × 24 + 5 = 7349.