When we do multiplication, we don’t need to worry anymore lining up our points.
We’ll figure out what the location of our decimal point is when our multiplication problem will be over.
Next Lesson: Fractions and Decimals in Order (MUST KNOW)
The transcript is for your convenience.
No More Lining-up
Well, when we can do multiplication of 2 and 3-digit numbers, we already can multiply decimals. Do you remember that we had to write in a few zeros (0’s) on our decimals to line them up? Well, here we don’t need to do those things anymore.
Let’s take a look here at one simple problem:
14.32 x 0.21 equals ?
First, begin by taking a look at the problem as a whole. We have actually just simple multiplication. We added a 0 (zero) when we began to multiply our values from the 10’s (tens) column. We then had to add up both our answers to get to our final answer. Now, how about our decimal points? When we figure out our final answer in decimals, we’ll have to factor in the total number of decimal points and place it in.
In our example, 14.32 includes two (2) numbers or places to the right of the decimal point while 0.21 has also two (2) places or numbers after its decimal point. So in total, we have four (4) places after our decimal points. Now when we’re done with our numbers, simply count four places left and place the decimal there. So the answer was here 30072, but after adding our decimal point, our final product would be 3.0072. So now you see that there are (4) four places to the right of, or after, our decimal point in our answer.
0.833 x 0.3 equals ?
First, solve the multiplication: 833 times 3 equals 2499
Secondly, we need to count all places after our decimal points in our factors: 4 (four) places
Then write our new decimal point 4 (four) places left in our answer
The answer is: 0.2499
Please note that when working with decimals in the metric system, we commonly write a zero in our answer first so readers know the value will be less than 1 (one). This makes reading easier than if we would start writing our number with a period or a dot.
The Metric System explained
Decimals form the core of our metric system that we use in science. We’ll introduce you to metric measurements later in our numbers sections. Now, let’s take a look at an example of how scientists use measurements:
We require an amount of one chemical for an experiment. We have five (5) test tubes and each tube contains 0.65 grams of the chemical compound. How much of the compound do we require in total?
Well, five (5) test tubes times 0.65 grams each is the total amount of grams needed.
So: 5 times 0.65 equals?
Or: 0.65 x 5 = ?
Simple multiplication: 3.25
So we will require 3.25 grams of the chemical compound for conducting our experiment. We came to our answer by simple multiplication after which we added our decimal point 2 (two) places in to the left. So when we’re doing multiplication, we won’t have to worry anymore lining up our points. We can figure out what the location of the decimal point is once we’ve solved the multiplication problem.