As it is usual to learn the product of numbers up to 12 times 12, I have extended the table thus far. In my opinion, all pupils who shew a tolerable capacity should slowly commit the products to memory as far as 20 times 20, in the course of their progress through this work.

If you have any doubt as to this expression, recollect that it means “contains more than two eighteens, but not so much as three.”

Among the even figures we include 0.

Including both ciphers and others.

For shortness, I abbreviate the words greatest common measure into their initial letters, g. c. m.

Numbers which contain an exact number of units, such as 5, 7, 100, &c., are called whole numbers or integers, when we wish to distinguish them from fractions.