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# 1 3 & 1-4 rounding

## on Sep 13, 2010

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## 1 3 & 1-4 roundingDocument Transcript

• 1-3 Estimating by Rounding Up or Rounding Down
1-4 Estimating by Rounding to the Nearest
Round any decimal up or down.
Round any decimal to the nearest value of a decimal place.
On August 29, 2005, Hurricane Katrina
ripped through Louisiana with a Category
5 storm. The hurricane caused severe
devastation in 80% of the major coastal
cities. The damage was estimated at
\$76 billion, and about 1,600 people lost
their lives.
What are some other examples
of a situation where an estimate might
be preferred over an exact value?
• Why are estimates needed?
1.An exact value may not be worth the trouble it would take to get it.
For example:
About 30,000 people attended the baseball game.
2.An estimation is often easier to work with than the exact value.
For example:
Instead of multiplying \$169.95, let's use \$170.
3.It may be safer to use an estimate than to try to use an exact value.
For example:
The home repairs will cost at least \$18,000 as a result of the hurricane. So we will budget \$20,000 to play it safe.
4.An exact value may change from time to time, forcing an estimate.
For example:
I estimate that the coin will land tails 5 times in 10 tosses.
5. Predictions of the future or notions about the past usually are estimates, since exact values may be impossible to obtain.
For example:
One estimate of the world population in the year 2025 is 12 billion.
• 4 Methods of Rounding
**Rounding is the most common way of estimating.**
*Rounding is done with a particular decimal place in mind.**
Rounding UP - "to the next;" going to the higher point of the interval
Rounding DOWN - "to the preceding;" going to the lower point of the interval
Truncate - round down, or cut off
1325
1400
1300
900
1325 Truncated to the tens place: 1320
**Some calculators truncate long decimals to the preceding millionth (6 decimal place).
For example:
π = 3.1415926535
a calculator might truncate it to show 3.141592
Rounding to the NEAREST - given a decimal place, look to the value after it:
if the value is 5 or greater, round up to the next number
if the value is 4 or less, truncate
Round 1325 to the nearest ten:
1330
Round 1325 to the nearest thousand:
1000
• Round up or down.
Example 1:
Round 10.4554 up to the next ten.
Round 10.4554 down to the previous tenth.
• Round to the nearest.
4 or less, round down (truncate)
5 or greater round up (next)
Example 2:
465,877,912.556 734 603
Round to the nearest million.
Round to the nearest tenth.
Round to the nearest ten thousandths.
Round to the nearest unit.
• What method should you use?
Example 3:
A certain type of CD-RWs are available only in 15 count packages. How many packages would you need to buy if you were to make a copy of your debut performance for each of your 110 classmates?
Example 4:
A cargo plane can carry 10,500 lbs. What weight limit may be placed on the cargo to be sure that the actual limit is not exceeded?
Example 5:
Pencils are sold in packages of 10. I need one pencil for each student in a class of 27.
How many pencils must be bought?
Example 6:
The product of 0.1349 and 0.00024 is 0.000032376. What will a calculator with an 8-digit display and that rounds show for the answer?
Example 7:
My savings account earns monthly interest. My bank rounds down any fractions of a
cent on interest paid on a savings account. How much interest would be paid if the calculated amount is \$75.625?
Example 8:
Giant Eagle sells avocados at three for \$1. You want just one. So you divide \$1.00
by 3 to get the cost. Your calculator shows 0.333333. How must will you probably
have to pay for the avocado?
Example 9:
The U.S. Interval Revenue Service allows taxpayers to round all amounts to the nearest dollar. In figuring income tax, to what value can you round each amount?
a. \$89.46 b. \$165.50 c. \$100.91 d. \$5,324.28
Example 10:
Avatar blue-ray costs \$27.49 and John wants to buy 7. How he can use rounding to estimate the cost?
Example 11:
The total U.S. population as of 3:04pm on Sunday, September 12, 2010, was
310,230,947. Round this number to the nearest ten thousand.
• Tonight's Homework/Practice:
Lesson Master 1-3A
Lesson Master 1-4A