138
Year review: multi-digit numbers, addition and subtraction
Textbook: Part 4, lesson 138, pp. 89–90
GoalYear review: classes and places, writing and comparing big numbers, addition and subtraction.
New words
class (of digits) · sinfplace · xonamillion · milliondifference · ayirma
Explanation
Numbers are split into classes: the units class, the thousands class and the millions class; each class has three places. When reading a number we say the class names: 7 305 048 is seven million three hundred five thousand forty-eight. To compare numbers we first compare the number of places and then the digits from the left. In column addition and subtraction we start from the units. Order of operations: brackets first, then multiplication and division, then addition and subtraction.
Worked examples
7 million 305 thousand 48 in digits: 7 305 048. The thousands class holds 305 and the units class holds 048.
438 215 + 56 790 − 19 005: first 438 215 + 56 790 = 495 005, then 495 005 − 19 005 = 476 000.
Class activity
“Digit cards”: each group makes the largest and the smallest seven-digit number from 7 digit cards, reads them aloud and finds their difference in a column.
Practice
1
Write 5 million 40 thousand 7 in digits.
5040007
2
Compare 630 450 and 630 405. By how many units is the larger number greater?
45
3
Calculate 8 507 321 − 2 649 880.
5857441
4
Find the value of (7 000 − 12 × 250) : 4.
1000
5
18 450 spectators came to a stadium on the first day and 3 275 more on the second day. How many spectators came in the two days?
40175