mathematics

National conventions for writing telephone numbers

National conventions for writing telephone numbers is a mathematics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand National conventions for writing telephone numbers rather than just read about it. In short: National conventions for writing telephone numbers vary by country. The International Telecommunication Union (ITU) publishes a recommendation entitled Notation for national and international telephone numbers, e-mail addresses and Web addresses.

Key takeaways

National conventions for writing telephone numbers belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect National conventions for writing telephone numbers to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of National conventions for writing telephone numbers from memory before moving on to harder problems.

Reference excerpt

National conventions for writing telephone numbers vary by country. The International Telecommunication Union (ITU) publishes a recommendation entitled Notation for national and international telephone numbers, e-mail addresses and Web addresses. Recommendation E.123 specifies the format of telephone numbers assigned to telephones and similar communication endpoints in national telephone numbering plans. In examples, a numeric digit is used only if the digit is the same in every number, and letters to illustrate groups. X is used as a wildcard character to represent any digit in lists of numbers.

Africa

Djibouti All telephone numbers in Djibouti have eight digits. Fixed line numbers start with 21 or 27, then a fixed line locality code, followed by four digits. Mobile numbers start with 77, then a mobile line locality code, followed by four digits. With the country code of Djibouti (253), the international format is "+253 XX YY ZZZZ".

Kenya Telephone numbers in Kenya use a 9-digit format. The nine digits used for local calls start with a "0" (trunk prefix) for domestic calls, followed by the 3-digit area/provider code and the final six digits (07XX XXX XXX). The international code for Kenya is "+254".

Morocco All telephone numbers in Morocco have ten digits (initial 0 plus nine numbers). Landline numbers start with 05, followed by two digits for the regional area RR, then two digits for the local area LL, then 4 digits for the subscriber number XX XX: ("05 RR LL XX XX" or "05RR LL XX XX"). Mobile numbers start with 06 or 07, followed by the subscriber number ("06 XX XX XX XX" or "07 XX XX XX XX"). The country code for Morocco is 212, so the format becomes "+212 Y XX XX XX XX" or "+212 YXX XX XX XX", also "+212 YXX-XXXXXX" as well, where Y is 5 for landlines or 6/7 for mobile. Free calling numbers (green numbers) or call center numbers start with 080 or 090.

South Africa South Africa uses 10-digit dialling, which has been required since 16 January 2007. The ten digits used for local calls (AAA XXX XXXX or 0AA XXX XXXX) consist of a 3-digit area/type code (the first digit in the area/type code is a trunk prefix) followed by seven digits. All area codes, including mobile numbers, start with a "0" (trunk prefix) for domestic calls. When dialing from another country, the country code for South Africa is "27", with the rest of the digits excluding the "0" trunk prefix (+27 AA XXX XXXX).

Asia

China Telephone numbers in China have 10 or 11 digits (excluding an initial zero which is required at times) and fall in at least four distinct categories:

Landlines: In China, the length of phone numbers varies from city to city. It is usually written as (0XXX) YYY YYYY (For landlines registered in large metropolises, it is written in the format (0XXX) YYYY YYYY), where 0 is the trunk code, XXX is the area code (2 or 3 digits) and YYYY YYYY is the local number (7 or 8 digits). For example, (0755) XXXX YYYY indicates a Shenzhen number. XXXXYYYY is dialed locally, 0755 XXXX YYYY is dialed in other areas inside the country, while, for international calls to Shenzhen, the 0 is dropped and is written +86 755 XXXX YYYY. Mobiles: The 11-digit code is always written in full in the whole China e.g. 1WX YYYY ZZZZ. Each WX is assigned to a service provider while W is usually '3' through '9'. The remaining eight digits are the subscriber number. Toll Free: These are usually ten digit numbers beginning with 800 or 400. 800 (toll-free) are accessible only when called from landline phones, while 400 (shared toll) are accessible from all phones. 400 XXX XXXX or 800 XXXX XXXX. Service numbers: These are usually 3- to 5-digit numbers (e.g. Police is 110) used to access an emergency service (Fire 119, Ambulance 120, Police 110, Roadside assistance 12122) or a value-added service.

Hong Kong and Macau Every number, except special service numbers, is an 8-digit number; they are grouped as XXXX YYYY. There are no area codes.

India Telephone numbers in India have ten digits (excluding an initial zero which is required at times) and fall into at least four distinct categories:

Landlines: Written as AAA-BBBBBBB, where AAA is the Subscriber Trunk Dialing code (long-distance code) and BBBBBBB is the phone number. The total length of the Subscriber Trunk Dialing code and the phone number is ten digits. The Subscriber Trunk Dialing code can have from two digits (11 or 011) up to four digits. Mobiles: Written as AAAAA-BBBBB for ease of remembering (though the prefix is either 2-digits or 4-digits in the numbering plan). Mobile numbers which are not local need to be prefixed by a 0 while dialing, or by +91 (91 is the country code for India). A mobile number written as +91-AAAAA BBBBB is valid throughout India, and in other countries where the + is recognized as a prefix to the country code. Since 2015, calls from mobile phones to any other mobiles do not need to prefix with a 0. However, calls from landlines to non-local mobile numbers need to be prefixed with 0. Toll Free: These are usually ten digit numbers beginning with 1-800. Sometimes they are accessible (or are toll-free) only when called from the government-owned telephone corporation, BSNL/MTNL. Service numbers: These are usually three or four digit numbers (e.g. Emergency Number is 112) used to access an emergency service (Fire, Ambulance, Police, Roadside assistance) or a value-added service.

Iran All telephone numbers in Iran have 11 digits (initial 0 and ten digits). The first two or three digits after the zero are the area code. The possibilities are: (0xx) xxxx xxxx (for landlines), 09xx xxx xxxx (for cellphones) and 099xx xxx xxx (for MVNO). When making a call within the same landline area code, initial 0 plus the area code must be omitted. An example for calling telephones in the city of Tehran is as follows:

xxxx xxxx (within Tehran, via a landline) 021 xxxx xxxx (Outside Tehran, or via a cellphone) +98 21 xxxx xxxx (outside Iran) An example for mobile numbers is as follows:

09xx xxx xxxx (in Iran) +98 9xx xxx xxxx (outside Iran)

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with National conventions for writing telephone numbers

Start with the simplest possible case. Write down what National conventions for writing telephone numbers claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to National conventions for writing telephone numbers before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about National conventions for writing telephone numbers ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of National conventions for writing telephone numbers

In research: National conventions for writing telephone numbers appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses National conventions for writing telephone numbers in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: National conventions for writing telephone numbers is common in secondary-school and first-year university syllabi. It links to neighbouring topics Open standards, Telephone numbers, so understanding it makes those chapters shorter.
In everyday life: Look for National conventions for writing telephone numbers outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study National conventions for writing telephone numbers in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what National conventions for writing telephone numbers means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain National conventions for writing telephone numbers out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is National conventions for writing telephone numbers in simple terms?

Why does National conventions for writing telephone numbers matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study National conventions for writing telephone numbers?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on National conventions for writing telephone numbers.