Chapter 1: Our Number System 7WORLDLY WISDOM
In the United States, you separate periods with commas. In other countries, like Italy,
they’re separated by periods, and in others, like Australia, by spaces.You read each group of three digits as if it were a number on its own and then add the period
name. The number 425 is “four hundred twenty-five,” so if you had 425,000, you’d say “four
hundred twenty-five thousand.” The number 425,000,000 is “four hundred twenty-five million,”
and 425,425,425 is “four hundred twenty-five million, four hundred twenty-five thousand, four
hundred twenty-five.”CHECK POINT- Write the number 79,038 in words.
- Write the number 84,153,402 in words.
- Write “eight hundred thirty-two thousand, six hundred nine” in numerals.
- Write “fourteen thousand, two hundred ninety-one” in numerals.
- Write “twenty-nine million, five hundred three thousand, seven hundred eighty-two”
in numerals.
Powers of Ten
Each place in a decimal system is ten times the size of its neighbor to the right and a tenth the
size of its neighbor to the left. As you move through a number, there are a whole lot of tens
being used. You can write out the names of the places in words: the hundredths place or the ten-
thousands place. You can write their names using a 1 and zeros: the 100 place or the 10,000 place.
The first method tells you what the number’s name sounds like, and the other helps you have a
sense of what the number will look like.
You can keep moving into larger and larger numbers, and the naming system keeps going with
the same basic pattern. The problem is that those numbers, written in standard notation, take
up lots of space and frankly, don’t always communicate well. In standard notation, one hundred
trillion is 100,000,000,000,000. Written that way, most of us just see lots of zeros, and it’s hard to
register how many and what they mean.
There’s a shortcut for writing the names of the places called powers of ten. All of the places in our
decimal system represent a value that’s written with a 1 and some zeros. The number of zeros
depends on the place. The ones place is just 1—no zero. The tens place is 10, a 1 and one zero.
The hundreds place is 100, a 1 and two zeros. The thousands place has a value of 1,000 or a 1 and
three zeros, and on it goes.