106
Writing lengths as decimals (practice)
Textbook: Part 3, lesson 106, pp. 110–111
GoalMore practice writing lengths as decimals: changing units, adding lengths.
New words
convert to a unit · birlikka o‘tkazishsum of lengths · uzunliklar yig‘indisiperimeter of a triangle · uchburchak perimetriaccuracy · aniqlik
Explanation
To change a length into a decimal in another unit, remember 1 mm = 0.001 m, 1 cm = 0.01 m, 1 dm = 0.1 m. Write each part in the needed unit and add: 7 m 5 dm 4 cm 2 mm = 7 + 0.5 + 0.04 + 0.002 = 7.542 m. To add lengths, change the decimals into common fractions or add whole numbers in the same unit.
Worked examples
5 dm 7 mm = 5.07 dm, because 7 mm = 0.07 dm.
A triangle has sides 3.5 cm, 4.2 cm and 2.8 cm: perimeter 9 + 15/10 = 10 5/10 = 10.5 cm.
Class activity
“Book edges”: children measure the length and width of a textbook cover and a notebook cover to the nearest mm, write the lengths in cm as decimals and find the perimeter of each cover; a classmate checks.
Practice
1
Write 8 m 1 dm 6 cm 3 mm in metres as a decimal.
8.163
2
Write 5 dm 7 mm in decimetres as a decimal.
5.07
3
What part of 1 dm is 47 mm? Write it as a common fraction and a decimal.
47/100 = 0.47
4
A triangle has sides 3 cm 5 mm, 4 cm 2 mm and 2 cm 8 mm. Write its perimeter in centimetres as a decimal.
10.5
5
Write the sum 2 m 15 cm + 3 dm 6 cm in metres as a decimal.
2.51