How_To_Be_Good_At_Math

NUMBERS • ROUNDING 27

Rounding to different place values

Rounding to different place values will give us

different results. Let’s look at what happens to 7641

when we round it to different place values.

Rounding to significant digits

We can also round numbers to one or

more significant digits.

Estimating height

This robot is 165 cm tall.

TRY IT OUT

What is his height rounded

to the nearest 10 cm?

What is his height rounded

to one significant digit?

(See below.)

Answers on page 319

165 cm

The rounded number

is very close to the

original

7 6 4 1

7 6 4 0

7 6 0 0

ROUNDED TO THE 8 0 0 0

NEAREST 1000

Let’s look at the number 6346. The

most significant digit is the one with

the highest place value. So, 6 is the most

significant digit. The digit after it is less

than 5, so we round down to 6000.

The second significant digit is in the

hundreds. The next digit is less

than 5, so when we round to two

significant digits, 6346 becomes 6300.

The third significant digit is in

the tens column. If we round our

number to three significant digits, it

becomes 6350.

The higher the place

value we round to, the

more different the

result could be to the

original number

6 3 4 6

6 3 4 6

6 3 4 6

6 0 0 0

6 3 0 0

6 3 5 0

ROUNDED TO ONE

SIGNIFICANT DIGIT

ROUNDED TO TWO

SIGNIFICANT DIGITS

ROUNDED TO THREE

SIGNIFICANT DIGITS

In a four-digit number, rounding to the

most significant digit is the same as

rounding to the nearest 1000

This is the second

significant digit

We round using

this digit

We round with

this digit

This is the third

significant digit

ROUNDED TO THE

NEAREST 100

ROUNDED TO THE

NEAREST 10

ORIGINAL NUMBER

We use this

digit when

rounding

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