Key terminology:
Product: The answer when you multiply. Ex in the multiplication sentence 3x5=15, the product of 3x5 is 15.
Quotient: The answer when you divide. Ex. The quotient in the division sentence 2.4 ÷ 6 = 0.4, the quotient of 2.4 ÷ 6 is 0.4
Estimate: Close to an amount or value, but not exact.
The type of estimation we will be using is benchmarks. We look at which whole number the decimal is closest to in order to estimate its value. For example, if I have 2.73, I would estimate the value as 3, since 2.73 is closer to 3 than 2. If I have 1.47, I would estimate the value as 1, since 1.47 is closer to 1 than 2.
An example of when I may want to estimate like this is when I go shopping. It is easier to add the whole numbers in my head than it is decimals, so I estimate each cost to add together. This way I can be sure I don't go over budget when shopping.
If I bought the following items for each price I can estimate how much I will spend:
Bread: $1.47 which is about $1
Milk: $ 2.86 which is about $3
Ham: $14.97 which is about $15
Yogurt: $3.85 which is about $4
Mayonnaise: 3.68 which is about $4
toilet paper: $20.42 which is about $20
oranges: $6.42 which is about $6
If I add my estimates together, I get $53, which is close to the actual amount. If I add all of the actual amounts together, I get $53.67. Using benchmarks is the type of estimation that will get you the closest to the actual amount.
Using benchmarks can also be useful for multiplying and dividing decimals as well. For example:
The mass of 8 ping pong balls is 23.84 g. How much does 1 ping pong ball weigh?
I can say that 23.84 is close to 24. So I write the following sentence:
24 ÷ 8 = 3
Each ping pong ball weighs about 3 grams.
To multiply I can do something similar. For example, if 1 baseball has a mass of 143.985, What is the mass of 4 baseballs? I would write the following:
143.985 is closest to 144 so,
144 x 4 = 576
The mass of 4 baseballs is about 576 g.
Click on the following link to complete the assignment. Use estimates to find the answers.
https://forms.gle/6xnzCfN8e18vjo5c7
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