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| 9 Theory slides |
| 10 Exercises - Grade E - A |
| Each lesson is meant to take 1-2 classroom sessions |
Here are a few recommended readings before getting started with this lesson.
LaShay is fascinated by numbers and how she can buy her favorite things. She is currently saving money to buy a used 4K drone.
Help LaShay answer the following questions to support her math skills. Doing so will help her improve her saving plan.
Quotients | Exact Value | Use Compatible Numbers | Estimate |
---|---|---|---|
615÷8 | 76.875 | 640÷8 | 80 |
36÷11.25 | 3.2 | 36÷12 | 3 |
52.82÷4.75 | 11.12 | 50÷5 | 10 |
LaShay decides to use one of the all-time classic methods of saving money — a piggy bank! She then weighs it. All of the coins in the bank add up to 137.79 grams.
Divide the total weight of all the money in the piggy bank by the weight of a dime. Then, round the weight of a dime to a whole number.
When dividing decimals, the divisor is changed to a whole number. This requires multiplying the divisor and the dividend by the same power of 10. First, write the division using long division notation. The dividend is 58.46 and the divisor is 3.7.
Start by dividing the whole number part of the dividend by the divisor.
LaShay needs $279.99 to buy the drone. She has already saved $125.75 up to this point. She then decided to mow her neighbor's lawn to make the rest of money she needs. Her neighbor agrees to pay her $9.25 per hour.
Her grandfather, who used to be a beekeeper, tells LaShay the following.
So you want to approximate the number of bees in that hive huh? Well, count the number of bees that leave the hive in one minute. Then multiply it by 3 and divide by 0.014. |
Divide the decimal numbers. Make sure that the decimal point is placed correctly. Round the answer to two decimal places, if necessary.
When dividing decimals, the divisor is converted into a whole number by multiplying it by a power of 10. However, the dividend must also be multiplied by the same power of 10 to keep the value of the quotient the same. Now take a look at LaShay's piggy bank problem.
Dividend | Divisor | Quotient |
---|---|---|
3000 | 100 | 30 |
300 | 10 | 30 |
30 | 1 | 30 |
3 | 0.1 | 30 |
0.3 | 0.01 | 30 |
The numbers in the first columns get smaller downwards by a factor of 10. The same is true for the numbers in the second column. However, the quotient always stays the same. Therefore, when the dividend and divisor both increase by the same factor of 10, the quotient remains the same.
We know that the average cow produces about 47 pounds of milk per day. We also know that one gallon of milk weighs about 8.5 pounds. Let's divide the weight of milk produced by one cow by the number of pounds in one gallon. 47 ÷ 8.6 This quotient is equal to the number of gallons that one cow produces in one day. Let's round the divisor and the dividend so that they are compatible numbers. Start by rounding 8.6 to the closest whole number. 8.6 ≈ 9 Now, we are looking for a number that is close to 47 and is divisible by 9. 47 ≈ 45 Since 45 is close to 47 and it is a multiple of 9, we round 47 to 45. Now, we can estimate the quotient.
We found that one cow produces about 5 gallons of milk in one day.
Dylan has 4.6 gigabytes of storage available on his phone. The average size of a song is 0.005 gigabyte.
We need to divide the available space on Dylan's phone by the average size of a song to find the number of songs the phone can store. 4.6 ÷ 0.005 Dividing decimal numbers is easier if we multiply the divisor and the dividend by the same power of 10 so that the divisor is a whole number. In this case, we will multiply by 10^3, or 1000. 4.6 * 1000 & = 4600 0.005 * 1000& = 5 This means that 4.6 ÷ 0.005 is the same as 4600÷ 5. Let's now calculate it. We will place the first digit of the quotient in the hundreds place because 46 contains nine groups of 5.
This means that Dylan's phone can store 920 songs.
Zosia rewrites 137.28 divided by 0.64 as follows.
We are told that Zosia wants to find the quotient of 137.28 and 0.64 with the given procedure.
We want to find if she is correct. Dividing decimal numbers is easier if we multiply the divisor and the dividend by the same power of 10 so that the divisor is a whole number. In this case, we need to multiply by 100 because the divisor 0.64 has two decimal places. 137.28* 100 &= 13728 0.64* 100 &=64 This means that 137.28÷ 0.64 is the same as 13728÷ 64. We obtained a different answer than our friend. Our friend is not correct because she multiplied the divisor by 100 but divided the dividend by 100. Remember that we must multiply both the divisor and the dividend by the same number when using this method. The answer is then B.
The diagram shows how Ignacio divides two decimal numbers.
Let's examine the steps Ignacio followed.
The operations seem correct at first glance. Let's find the quotient ourselves to find out if it really is. In this case, we divide a decimal number by a whole number. This is why we divide as we would with whole numbers. We also place the decimal point in the quotient directly above its place in the dividend. Let's do it!
We put a zero in the tenths place because there is no group of 7 in 6. Then, we continue as usual. As a result, we obtained a different answer than our friend. The answer is A.