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# Rounding, Estimation, and Decimal Equivalents for CBEST Exam Study Guide (page 2)

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Updated on Mar 29, 2011

### Estimation

Estimation requires rounding numbers before adding, subtracting, multiplying, or dividing. If you are given numerical answers, you might just want to multiply the two numbers without estimation and pick the answer that is the closest. Most likely, however, the problem will be more complicated than that.

#### Sample Estimation Question

1. 42 × 57 is closest to
1. 45 × 60
2. 40 × 55
3. 40 × 50
4. 40 × 60
5. 45 × 50

Here's how you could use the Success Steps to answer the sample question:

1. You can round 42 down and 57 up, resulting in choice d.
2. Rounding the numbers to one significant digit yields d also.
3. Eliminate choices. a. Eliminated: 45 is further from 42 than 40 is. b. Maybe. c. Eliminated: 50 is further from 57 than 60 is. e. Eliminated: 45 is further from 42 and 50 is further from 57.
4. Check the remaining answers. The product of choice b is 2,200. The product of choice d is 2,400. The actual product is 2,394, which makes choice d the closest, and therefore the correct answer.

### Decimal Equivalents

You may be asked to compare two numbers to tell which one is greater. In many cases, you will need to know some basic decimal and percentage equivalents.

#### Decimal-Fraction Questions

See how many of these you already know. For questions 6–11, state the decimal equivalent.

For questions 12–14, determine which number is greater.

1.
1. 0.93
2. 0.9039
2.
1. 0.339
3.
1. 0.52

1. 0.5
2. 0.75
3. 0.8
4. 0.125
5. a. To compare these numbers more easily, add zeros after the shorter number to make the numbers both the same length: 0.93 = 0.9300. Compare 0.9300 and 0.9039. Then take out the decimals. You can see that 9,300 is larger than 9,039
6. Extending the number would yield . (A line over a number means the number repeats indefinitely.) The number 333 is less than 339.
7. Instead of dividing the denominator (91) into the numerator (45), look to see whether the two choices are close to any common number. You might notice that both numbers almost equal . 45 is less than half of 91, so is less than half. Half in decimals is 0.5 or 0.50; 0.52 is greater than 0.50, so it is greater than half. Thus, choice b is greater.

### Decimal-Percentage Equivalents

You may already know that when you deposit money in an account that earns 5% interest, you multiply the money in the bank by 0.05 to find out your interest for the year. 5% in decimal form is 0.05.

##### Hot Tip

To change a percent to a decimal, move the decimal point two places to the left. To change a decimal to a percent, move the decimal point two places to the right. If there is no decimal indicated in the number, it is assumed that the decimal is after the ones place, or to the right of the number.

The percent always looks larger than its decimal equivalent. Here are some examples:

 Number Written as a Percent 0.05 5% 0.9 90% 0.002 0.2% 0.0004 0.04% 3 300%

#### Questions

Rewrite the following numbers as percents.

1. 0.07
2. 0.8
3. 0.45
4. 6.8
5. 97
6. 345
7. 0.125

Rewrite the following percents as decimals.

1. 5%
2. 0.7%
3. 0.09%
4. 49%
5. 764%

1. 7%
2. 80%
3. 45%
4. 680%
5. 9,700%
6. 34,500%
7. 12.5%
8. 0.05
9. 0.007
10. 0.0009
11. 0.49
12. 7.64

### Common Equivalents

Here are some common decimal, percent, and fraction equivalents you should have at your fingertips. A line over a number indicates that the number is repeated indefinitely.