55
Long division by a two-digit number
Textbook: Part 2, lesson 55, pp. 51–53
GoalLong division of a three-digit number by a two-digit number.
New words
long division · burchakli bo‘lishrounding · yaxlitlashincomplete dividend · to‘liqsiz bo‘linuvchibringing down · pastga tushirish
Explanation
Algorithm: 1) take the smallest group of leading digits that the divisor can divide; 2) choose a quotient digit (rounding the divisor to tens helps to guess); 3) multiply, subtract, get the remainder; 4) bring down the next digit; 5) repeat until the digits run out. 756 : 12: 75 : 12 = 6 (72, remainder 3), 36 : 12 = 3. The quotient is 63.
Worked examples
1 058 : 23: 105 : 23 = 4 (92, remainder 13), 138 : 23 = 6. The quotient is 46.
Check: 23 × 46 = 1 058.
Class activity
“Estimation experts”: children round the divisor (23 ≈ 20), estimate the quotient, then do the real division and compare how close the guess was.
Practice
1
684 : 36 = ?
19
2
1 275 : 25 = ?
51
3
2 646 : 42 = ?
63
4
A family used 288 cubic metres of gas in a year. If it used the same amount each month, how many cubic metres per month?
24