Section 2C Formulas with Dividing Decimals

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1 Section 2C Formulas with Dividing Decimals x Look at the following z-score formula again from Statistics. z. Suppose we want to calculate the z-score if x 17.6 pounds, 13.8 pounds, and 2.5 pounds. Not only do we need to be able to subtract decimals, but we also need to be able to divide decimals. So let s review dividing decimals some. (This section is from Preparing for Algebra and Statistics, Second Edition by M. Teachout, College of the Canyons, Santa Clarita, CA, USA) This content is licensed under a Creative Commons Attribution 4.0 International license 26

2 Much like multiplying decimals, the key to dividing decimals is that we need to make sure to put the decimal in the correct place. We need to make sure that the number we are dividing by (divisor) is a whole number. If the divisor is a whole number then the decimal in the answer will be directly above where it is in the number we are dividing. That is pretty confusing, but I hope an example will help clear it up. Look at One thing to note is that the first number (dividend) always goes on the inside of the long division. The number you are dividing by (divisor) goes on the outside Since the divisor is not a whole number, we need to move the decimal one place to the right. We will have to move the decimal inside 1 place to the right as well. Hence the division becomes: Notice the dividend does not have to be a whole number. Only the divisor does. Now divide as if they are whole numbers. You may need to add zeros to the end of the dividend if it does not come out even Notice we keep adding zeros and dividing until we get a zero remainder or we see a repeating pattern. In this case we got a zero remainder after the thousandths place. Notice also the decimal is directly above where it is in the dividend. This again is only the case when the divisor is a whole number. We can also use estimation to see if the decimal is in the right place. 14 is slightly over half of 25, so the answer should be a little bigger than one-half (0.5). Occasionally we divide decimals by powers of 10 (10, 100, 1000, etc.) Remember when you multiply by a power of 10 the decimal simply moves to the right. It is similar with division. If you divide by a power of 10, you move the decimal to the left the same number of places as the number of zeros in your power of 10. For example moves the decimal 3 places to the left so is the answer. A good way to remember the left and right rules is to think of it as bigger and smaller. When we multiply by a number like 1000, we are making the number larger, so the decimal has to move to the right. When we divide by a number like 1000, we are making the number smaller, so the decimal has to move to the left. 27

3 Now you try some examples with your instructor. Example 1: Example 2: Example 3: Example 4: Fractions can also be converted to decimals simply by dividing the numerator by the denominator. Remember the denominator is the divisor and has to go on the outside of the long division. For example the fraction 5/8 is really 5 8, so if we add zeros to the 5 and divide, we get the following: Notice we did not have to move the decimal as our divisor 8 was already a whole number. 28

4 Try a couple more examples with your instructor. Example 5: Convert 3/16 into a decimal. Example 6: Convert 5/6 into a decimal. Place a bar over any repeating part. Practice Problems Section 2C Divide the following and write your answer as a decimal or whole number Convert 1/4 into a decimal. 32. Convert 2/3 into a decimal. 33. Convert 3/5 into a decimal 34. Convert 5/9 into a decimal. 29

5 35. Convert 3/8 into a decimal. 36. Convert 7/99 into a decimal. 37. Convert 3/25 into a decimal 38. Convert 7/24 into a decimal. 39. Jim works in construction and gets paid $ every four weeks. How much does he make each week? 40. Miko needs $ for a down payment on a home. If she can save $ each month, how many months will it take her to get the money she needs. (Not counting interest). Let s see if we can solve the z-score problem from the beginning of the section. Use the x formula z 41. Find the z-score if x 17.6 pounds, 13.8 pounds, and 1.6 pounds. 42. Find the z-score if x 73.1 inches, 69.2 inches, and 2.5 inches. The following formula calculates the volume of a cone in geometry. 2 V rh 43. Find the volume of a cone with a radius of 4 cm and a height of 1.2 cm. (Use 3.14 ) 44. Find the volume of a cone with a radius of 0.5 yards and a height of 2 yards. (Use 3.14 ) 3 30