الأسبوع 1 · الوحدة ١ «النظم العددية» (١): الرقم والعدد، النظام العشري، قيمة الخانة وقوى الأساس · 3 دروس
1
Digits and numbers: what is the difference?
ICT Secondary 3 Term 1, Unit 1, Topic 1: pp. 5–10
GoalTell a digit from a number and count the digits of a number.
New words
digit · one symbol written in one place of a numbernumber · one or more digits written togethersymbol · a mark such as 3 or A that stands for one valueplace · the position of a digit in a number, counted from the right
Explanation
In everyday talk “digit” and “number” sound like the same thing, but in computing they are different. A digit is one symbol sitting in one place, such as the 3 in 23. A number is one or more digits written together: 7 is a number with one digit, 38 is a number with two digits, and 6150 is a number with four digits. The same symbol can be a digit in one place and a whole number on its own: the 3 in 23 is a digit, but 3 written alone is a number. The place matters because it decides what a digit is worth: the 4 in 407 stands for four hundreds, while the 4 in 74 stands for four ones. The digit 0 is a digit like any other: in 407 it sits in the tens place and tells us that there are no tens. In the next lessons this idea will let us read numbers written with only two symbols, and then with sixteen.
Number
Its digits
How many digits?
7
7
1
38
3, 8
2
407
4, 0, 7
3
6150
6, 1, 5, 0
4
Worked examples
What she sees
Digits
Count
6150
6, 1, 5, 0
4
150
1, 5, 0
3
50
5, 0
2
0
0
1
Mona reads the number 6150 on a ticket. Its digits are 6, 1, 5 and 0, so it is a number with four digits. She covers the digits one by one from the left. What is left is a different number each time, because every digit takes its place with it.
Number
Digits
Digits counted
Different symbols
5
5
1
1
150
1, 5, 0
3
3
2505
2, 5, 0, 5
4
3
The digit 5 appears in the numbers 5, 150 and 2505. The first is a number with one digit, the second has three digits, the third has four digits with the digit 5 twice. We count digits, not different symbols: 2505 has four digits although it uses only three different symbols.
Class activity
On paper write five numbers with one, two, three, four and five digits. For each one list its digits from left to right. Circle every number in which the same digit appears twice.
Practice
1
How many digits does 3,947 have, and which digit is in the tens place?
Four digits: 3, 9, 4 and 7. The digit in the tens place is 4.
2
Is 8 a digit or a number?
Both: it is a digit when it sits in a place of a longer number, and a number with one digit when written alone.
3
Write a number with three digits in which the digit 0 appears twice.
For example 800: its digits are 8, 0 and 0.
4
Do 2015 and 5102 use the same digits? Are they the same number?
They use the same digits (2, 0, 1 and 5) but in different places, so they are different numbers.
