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Frequent learner mistakes involving numbers, dates and time.
Use cardinal numbers to express quantity and ordinal numbers to express position or sequence.
For example, three books expresses quantity, while the third book identifies position.
Hundred, thousand, million, billion, and similar units remain singular after an exact preceding number.
For example, three hundred people, five thousand dollars, and two million users.
Large number words take plural forms before of when the quantity is indefinite.
For example, hundreds of people, thousands of users, and millions of dollars.
The correct spelling of 40 is forty, and related forms use the same spelling base.
For example, forty, forty-two, and fortieth.
Several common ordinal forms have irregular spellings that must be memorized.
The correct forms are fifth, eighth, ninth, and twelfth.
Ordinal forms of tens change the final y to ieth.
For example, twentieth, thirtieth, fortieth, and fiftieth.
Ordinal abbreviations use the correct final suffix according to the number, with special treatment for 11, 12, and 13.
For example, 21st, 22nd, 23rd, 24th, but 11th, 12th, and 13th.
A number of means several and takes a plural verb, while the number of refers to the quantity and normally takes a singular verb.
For example, A number of people are waiting, but The number of people is increasing.
Verb agreement depends on the grammatical noun phrase being referred to rather than mechanically matching the numerical expression.
For example, Two students are absent, but One student is absent.
Zero normally takes plural countable nouns.
For example, zero mistakes, zero students, and zero dollars.
One normally takes a singular countable noun.
For example, one book, one student, and one mistake.
Few is used with plural countable nouns, while little is used with uncountable nouns.
For example, few people but little information.
Fewer is normally used with plural countable nouns, while less is normally used with uncountable nouns.
For example, fewer problems but less time.
A few indicates a small but real number, while few emphasizes that the number is small or insufficient.
For example, A few people came versus Few people came.
A little indicates a small but real amount, while little emphasizes that the amount is very small or insufficient.
For example, We have a little time versus We have little time.
British English commonly uses day-month-year order, while American English commonly uses month-day-year order.
For example, 15 August 2026 versus August 15, 2026.
Purely numeric dates can be interpreted differently across regional conventions.
For example, 04/05/2026 may represent 4 May or April 5.
On is normally used before a specific day or calendar date.
For example, The meeting is on 15 August and We arrived on Monday.
In is normally used with months and years when referring to a period rather than a specific day.
For example, in August and in 2026.
Expressions containing this, last, next, or every normally do not require an additional preposition before the time expression.
For example, next Monday, last year, this morning, and every Friday.
Century names are one number higher than the first two digits of most years within that century.
For example, 1901 begins the twentieth century and 2001 begins the twenty-first century.
The 1900s commonly identifies 1900–1909, while the twentieth century identifies 1901–2000.
These expressions should not be treated as exact synonyms.
The 2020s refers to 2020–2029, while the twenty-first century refers to 2001–2100.
A decade and a century are different periods even when their names overlap numerically.
Fully written decade names are pluralized without an apostrophe.
For example, the 1980s and the 1990s, not the 1980's and 1990's.
Years are normally read using conventional year pronunciation patterns rather than automatically reading every digit separately.
For example, 1984 is nineteen eighty-four and 2026 is twenty twenty-six.
Digits after a decimal point are normally read individually.
For example, 3.14 is three point one four.
Zero should be pronounced when needed to distinguish digits after the decimal point.
For example, 2.05 is two point zero five.
Percent follows a numerical value, while percentage is normally used as a noun.
For example, twenty percent of users and What percentage of users?
A difference between percentages measured in percentage points is not the same as a relative percentage increase.
For example, 20% to 25% is five percentage points but a twenty-five percent relative increase.
Verb agreement after a fraction depends on the noun phrase being measured.
For example, half of the cake is gone, but two thirds of the students are absent.
Verb agreement after a percentage depends on the noun following of.
For example, Forty percent of the employees are remote, but forty percent of the equipment is unused.
Measurement units remain singular when they form part of a compound modifier before a noun.
For example, a five-year-old child, a two-metre wall, and a ten-kilometre race.
Numbers used as addresses, room numbers, flight numbers, and similar identifiers are not necessarily read as ordinary mathematical quantities.
For example, Flight 205, Room 12, and Bus 7 are identifier expressions.
Telephone numbers are normally read as individual digits or convenient groups, with zero sometimes pronounced as oh.
For example, 507 can be read as five-oh-seven.
Correct number usage requires control of cardinal and ordinal forms, large-number grammar, dates, time, fractions, decimals, percentages, measurements, agreement, and contextual pronunciation.
Before choosing a numerical form, identify whether the number expresses quantity, order, measurement, date, time, proportion, ranking, or identification.