11
The place-value number system
Textbook: Part 1, lesson 11, pp. 34–36
GoalUnderstand the place-value system: the value of a digit depends on its position.
New words
digit · raqamplace-value number system · pozitsion sanoq sistemasiArabic numerals · arab raqamlariRoman numerals · rim raqamlari
Explanation
We write every number with 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. These digits were invented in India, and the invention of zero was especially important. The value of a digit depends on its position: in 528, 5 is hundreds, 2 is tens, 8 is ones. In old Europe Roman numerals were used: I = 1, V = 5, X = 10, L = 50, C = 100.
Worked examples
528 has 5 hundreds, 2 tens and 8 ones; there are 52 whole tens and 5 whole hundreds.
LVIII = 50 + 5 + 3 = 58; CXII = 100 + 10 + 2 = 112.
Class activity
“Digit cards”: three children hold the cards 2, 5 and 8. They stand in different orders to make three-digit numbers and read each one.
Practice
1
How many digits do we use to write numbers?
10
2
How many different three-digit numbers can be made from the digits 2, 5 and 8, using each once?
6
3
How many whole tens are there in 528?
52
4
Calculate XXVII + XII and give the answer in Arabic numerals.
39
5
3 magnets cost 60 000 so‘m. How much do 5 magnets cost?
100000