67
Chapter VII review problems
Textbook: Part 2, lesson 67, pp. 126–129
GoalReview of Chapter VII: operations with decimals, rounding, percents.
New words
decimal · o‘nli kasrrounding · yaxlitlashpercent · foizmoving the point · vergulni surish
Explanation
In addition and subtraction of decimals, the points are written under each other. In multiplication we multiply ignoring the points and separate as many digits as the two factors have after the point together. In division we move the point the same number of places in both numbers to make the divisor a natural number. When multiplying by 10, 100, 1000 the point moves right, when dividing it moves left. For rounding we look at the first dropped digit. Percent is one hundredth: to find p percent of a number, multiply the number by p/100.
Worked examples
(8.4 + 3.6) : 0.4 = 12 : 0.4 = 120 : 4 = 30. 25% of 12.8: 12.8 · 0.25 = 3.2.
Round 4.0678 to hundredths: the first dropped digit is 7, so the 6 becomes 7: 4.07. 0.4 · 0.5 = 0.20 = 0.2, which is less than 0.4 because 0.5 < 1.
Class activity
“Chapter map”: on one sheet, write the main rules of the chapter (adding, subtracting, multiplying, dividing, rounding, percent), each with one example.
Practice
1
Calculate (8.4 + 3.6) : 0.4.
30
2
Round 4.0678 to hundredths.
4.07
3
Find 25% of 12.8.
3.2
4
Why is the product 0.4 · 0.5 smaller than 0.4?
We multiplied 0.4 by a number less than 1 (0.5), so only a part of it remains.