Reading numbers by their places

This lesson asks you to read, build and take apart whole numbers up to 10 000, and to say where such numbers are used in everyday life. The museum offers one thing here, a record on how numbers are written by place value; your class brings the everyday uses and the practice. ¹

Take the same digit in the ones place and in the thousands place and compare what each is worth. Then show how a number is built from the worth of its places, and taken apart again.

The numerals in al-Khwarizmi's book did not begin in Baghdad. They are Indian, as their name says, and Indian reckoning had already come to Baghdad before him, in astronomy ². TDV records that around 154 AH (770–771 CE) an Indian delegation came to Baghdad, under the caliph Abu Ja'far al-Mansur, bringing Brahmagupta's Siddhanta, or a work of the same name derived from it ². On that book rest the Sindhind tables that al-Khwarizmi himself later made ².

A book came from India to Baghdad, and later a scholar in Baghdad wrote about calculating with the Indian numerals. Why is it useful to know how an idea travelled, and not only where we use it today?

• Algorism: how the Indian numerals and the place-value way of writing reached the Islamic world.
• al-Khwarizmi's Sindhind tables: the astronomical tables built on the Indian book.
• al-Khwarizmi: where he came from and where he worked.

Read the record Algorism. Write a four-digit number, say what each digit is worth by its place, and take the number apart into thousands, hundreds, tens and ones.