We will solve the multiplication of decimal numbers using the vertical multiplication method. We will proceed in the following order:
We will neatly write the multiplication exercise in vertical form โ one decimal point under the other decimal point, tenths under tenths, hundredths under hundredths, etc.
We will solve the exercise and, for now, will not pay attention to the decimal point.
We will strictly adhere to the rules of vertical multiplication.
We will review each number in the exercise and find out how many digits there are after the decimal point.
We will count the total number of digits after the decimal point (taking into account both numbers) and that will be the number of digits after the decimal point in the final answer.
Test yourself on multiplication of decimal fractions!
\( 0.1\times0.004= \)
Incorrect
Correct Answer:
\( 0.0004 \)
Practice more now
Multiplication of Decimal Numbers
To easily solve exercises involving the multiplication of decimal numbers, you should know how to solve multiplications of whole numbers using the vertical form. The most recommended method for solving exercises of this type is, clearly, multiplication in vertical form. Steps to follow:
โข We will write the exercise clearly in vertical form โ decimal point under the other decimal point, tenths under tenths, hundredths under hundredths, and so on.
โข We will solve the exercise without taking the decimal point into account, but remembering that it exists.
โข Let's not stop acting according to the rules of multiplication in vertical form, that is, reserving places for zeros, carrying over remainders and remembering them, etc.
โข We will count the total number of digits after the decimal point (taking into account both numbers) and in this way determine the number of digits that will be after the decimal point in the result.
Let's apply the solution steps in an exercise, this will help you understand it better: Given the exercise 0.4ร0.2= We will write it in vertical form making sure that the decimal point is under the other decimal point:
Let's solve the exercise as we always do, remembering the rules of multiplication in vertical form.
Notice: for now we ignore the decimal point and do not note it in the result. We obtained the result 008 How will we know where to place the decimal point in the result? Let's look at the numbers in the exercise and add up the number of digits after the decimal point in both numbers.
What does this mean? Let's look at the first number 0.4, there is one digit after the decimal point. Let's look at the second number 0.2, there is one digit after the decimal point.
Let's ask: How many digits after the decimal point are there in total? 2 1+1=2
Therefore, there will be 2 digits after the decimal point in the result. We will obtain:
And this is the final result.
Multiplication Exercises with Decimal Numbers
Exercise 1
0.02ร0.09=
Solution: We will write the exercise in vertical form making sure that the decimal point is under the other decimal point:
We will solve it as usual, ignoring the decimal point:
Let's add up the number of digits after the decimal point in the numbers of the exercise and apply the result in the final answer:
Let's apply this to the result and we will get 0.0018 :
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Test your knowledge
Question 1
\( 0.1\times0.35= \)
Incorrect
Correct Answer:
\( 0.035 \)
Question 2
\( 0.1\times0.5= \)
Incorrect
Correct Answer:
\( 0.05 \)
Question 3
\( 0.1\times0.999= \)
Incorrect
Correct Answer:
\( 0.0999 \)
Exercise 2
45.7ร0.4=
Solution: Let's write the exercise clearly in vertical form. Let's solve it as usual and ignore the decimal point. We will obtain:
Let's calculate where to place the decimal point:
Let's apply it to the answer and we will obtain: 18.28
Exercise 3
15.06ร0.01=
Solutionื: Let's write the exercise clearly in vertical form. Let's solve it as usual and ignore the decimal point in the result. We will obtain:
Let's calculate where to place the decimal point:
Let's apply it in the answer and we will obtain: That is, 0.1506
Do you know what the answer is?
Question 1
Find the correct place of the decimal point:
\( 1.35\times2.47=33345 \)
Incorrect
Correct Answer:
\( 3.3345 \)
Question 2
Given the following exercise, find the correct place of the decimal point:
\( 2.5\times0.13=0325 \)
Incorrect
Correct Answer:
\( \text{0}.325 \)
Question 3
Given the following exercise, find the correct place of the decimal point:
\( 3.751\times0.5=18755 \)
Incorrect
Correct Answer:
\( 1.8755 \)\( \)
Exercise 4
13ร0.24=
Solution: Let's write the exercise clearly in vertical form. Let's solve it as usual and ignore the decimal point in the result.
We will obtain:
Let's calculate where to place the decimal point:
Let's apply it in the answer and we will obtain: 03.12ย That is, 3.12
Examples and exercises with solutions for multiplying decimal numbers
Exercise #1
0.1ร0.004=
Video Solution
Step-by-Step Solution
To solve this problem, we'll multiply the decimals as follows:
Step 1: Multiply the whole numbers 1 and 4. This gives us 4.
Step 2: Count the total number of decimal places in the factors. 0.1 has 1 decimal place, and 0.004 has 3 decimal places.
Step 3: In the final answer, place the decimal point to ensure our product has 1+3=4 decimal places.
Now, let's apply these steps:
First, multiply 1 by 4 to get 4. Then place the decimal in the product so it has 4 decimal places: 0.0004.
Therefore, the solution to the problem is 0.0004.
Answer
0.0004
Exercise #2
0.1ร0.35=
Video Solution
Step-by-Step Solution
To solve this problem, we'll follow these steps:
Step 1: Convert the decimal numbers into a form that is easier to multiply.
Step 2: Multiply the numbers as if they were whole numbers.
Step 3: Adjust the product by placing the decimal point correctly.
Now, let's work through each step:
Step 1: Convert the decimals 0.1 and 0.35 into whole number expressions:
0.1 can be thought of as 101โ.
0.35 can be thought of as 10035โ.
Step 2: Multiply as whole numbers: Multiply 1 and 35 to obtain 35.
Step 3: Adjust the decimal point:
0.1 has 1 decimal place.
0.35 has 2 decimal places.
Thus, their product should have 1+2=3 decimal places.
Therefore, the product of 0.1 and 0.35 is 0.035.
Looking at the choices provided:
Choice 1: 0.35 is incorrect as it does not consider the decimal adjustment.
Choice 2: 0.035 is correct.
Choice 3: 0.350 is incorrect as it has an extra zero and maintains the incorrect placement of the decimal point.
Choice 4: 0.310 is incorrect as it does not correspond with the straightforward multiplication of the operands.
Thus, the correct choice is 0.035.
Answer
0.035
Exercise #3
0.1ร0.5=
Video Solution
Step-by-Step Solution
To solve this problem, we'll multiply the decimal numbers 0.1 and 0.5, following these steps:
Step 1: Treat each number as if it were a whole number and multiply: 1ร5=5.
Step 2: Count the decimal places in both factors. The number 0.1 has one decimal place, and 0.5 also has one decimal place.
Step 3: The total number of decimal places in the product should be the sum of the decimal places in the factors, which is 1+1=2.
Step 4: Place the decimal point in the product 5, resulting in 0.05, to ensure it has two decimal places.
Therefore, the product of 0.1 and 0.5 is 0.05.
Answer
0.05
Exercise #4
0.1ร0.999=
Video Solution
Step-by-Step Solution
To solve 0.1ร0.999, we need to follow these steps carefully:
Step 1: Treat the numbers as integers and multiply them. Ignoring the decimal points temporarily, multiply 1 by 999: 1ร999=999.
Step 2: Determine the total number of decimal places in the factors. 0.1 has 1 decimal place. 0.999 has 3 decimal places.
Therefore, the product should have 1+3=4 decimal places.
Step 3: Position the decimal in the product calculated in step 1. 999 with 4 decimal places becomes 0.0999.
Therefore, the product of 0.1ร0.999 is 0.0999.
Answer
0.0999
Exercise #5
Find the correct place of the decimal point:
1.35ร2.47=33345
Video Solution
Step-by-Step Solution
To solve this problem, we will place the correct position for the decimal point in the product of 1.35 and 2.47.
Let's follow these steps:
Step 1: Identify the number of decimal places in the numbers being multiplied. 1.35 has 2 decimal places, and 2.47 also has 2 decimal places.
Step 2: Add these decimal places: 2+2=4. So, the product should have 4 decimal places.
Step 3: The given product without considering the decimal point is 33345. We need to position the decimal so that the product has 4 decimal places.
Now, let's work through applying these steps:
Step 1: 1.35 and 2.47 each contribute 2 decimal places.
Step 2: We sum 2+2 to get a total of 4 decimal places for the final result.
Step 3: Place the decimal point in 33345 so that there are four digits after the decimal point. This gives us 3.3345.
Therefore, the correct placement of the decimal point in 33345 is 3.3345.
Answer
3.3345
Check your understanding
Question 1
Given the following exercise, find the correct place of the decimal point:
\( 6.13\times2.05=125665 \)
Incorrect
Correct Answer:
\( 12.5665 \)
Question 2
Look at the following exercise and determine the correct place of the decimal point:
\( 3.5\times2.4=840 \)
Incorrect
Correct Answer:
\( \text{8}.40 \)
Question 3
Look at the following exercise and work out the correct place of the decimal point in the answer: