In this lesson we're going to learn multiplying and dividing decimals. Difficulty of multiplying and dividing decimals are same as adding and subtracting decimals. Also the steps are similar as multiplying and dividing the whole number.
When you're multiplying decimal, if you're confused with the decimal point,
erase the decimal point for a while then put the decimal point when the calculation is done.
After you finished your calculation of multiplying decimals, add how many places did decimal point moved on each decimal and add all the positions.
Our first example is "Find 1.63 x 4.2."
Like we did on adding and subtracting decimals, we do it in easy way.
a
163
x 42
326
+ 652
6846
After the calculation is over, we put the decimal points.
When you're putting the decimal point, you need to make sure that the answer has the same number of decimal places as the question.
Therefore, 2 in 1.63 and 1 in 4.2, the total is 3 therefore our answer is 6.846.
Second example is " Find 0.4 of $5.60."
There are two way s to work out this question. You either go directly 0.4 times 5.60, or change the unit of $5.60 into 560 cents. The answer is same on which method you use.
Method 1 is 0.4
x 5.60
Therefore our answer is $2.24.
Method 2 is $5.60 is 560 cents, so 0.4 equals to 4/10
4/10 x 560 equals to 224, in dollar, is $2.24.
In Dividing decimal, we do the same thing as we did it in multiplying decimal but the working out is different.
Example 1 is " Evaluate 6.47/5."
1.294
5 6.47
5
1.4
1.0
47
45
20
Therefore our answer is 1.294.
Second example is "Find 52.16/0.4."
Firstly, we need to make 0.4 to whole number, and is 4.
Also we need to make sure that 52.16 turns into 521.6.
Reason is 0.4 moved to right to make a whole number, therefore the other decimal point must be moved to right.
130.4
4 521.6
4
12
12
1.6
1.6
0
Therefore our answer is 130.4.
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