Rounding Numbers

Rounding NumbersRounding means reducing the digits in a number while trying to keep its value

similar.

The result is less accurate, but easier to use.

Common Method: • Decide which the last digit to keep

– Leave it the same if the next digit is les than 5 (this is called rounding down)– Increase it by 1 if the next digit is 5 or more (this is called rounding up)

• Every place number less than the last digit is replaced with zeros

Examples:

1. Round 174 to the nearest 10.

2. Round 1.2635 to the tenths place.174Last Digit to Keep

Less than 5

170Keep it the same

1.2635Last Digit to Keep

5 or More

1.3Increase it by 1

AP Calculus Rule for Rounding

Always round to three decimal

places.

1.2635Last Digit to Keep

5 or more

1.264Increase it by 1

START FOLLOWING

THIS RULE NOW!

Example:

Contextual RoundingBe aware that there are instances where the type

of rounding is determined by the context:

Example: A can of paint covers 100 square feet. If Ryan needs to paint 925 square feet, how many cans of paint should he purchase?

Example: Elizabeth can write 53 words in one minute. How many complete words can she write in 30 seconds?

925÷100=9.25 10 cansYou must round to a

whole number, but using our method of rounding to 9 cans would be too few to paint the entire room.

Round up.

53÷2=26.5 26 wordsYou must round to a

whole number, but using our method of rounding to 27 words is not true (she can not write that many).

Round Down.