Question Video: Multiplying a Percent by a Decimal Mathematics • 7th Grade

Calculate 25% × 0.2. Give your answer as a decimal number.


Video Transcript

Calculate 25 percent times 0.2. Give your answer as a decimal number.

Let’s consider two different ways to find this product. First, we’ll take 25 percent time 0.2, and we’ll rewrite 25 percent as a decimal. We know that 25 percent is 25 out of 100. Another way to say that would be twenty-five hundredths. You could also imagine that we have moved the digits two places to the right. Anyway, we have a decimal value of 0.25, which we need to multiply by 0.2.

We could rewrite this vertically and say that two times five is 10, two times two is four plus one is five, two times zero is zero. And then our second row would be all zeros: zero times five, zero times two, and zero times zero. Then, we’ll add the partial products. Then, there are three decimal places in the multiplication, and that means the solution will have three decimal places, which will be 0.05. Now, there was a zero behind the five, but 0.050 can be simplified to 0.05. And that means in simplest form, we would say 0.05. This means 25 percent time 0.2 is equal to 0.05. 25 percent times 0.2 is equal to 0.05.

Let’s look at a second option. What if we said 25 percent we knew was equal to one-fourth. And 0.2 written as a fraction is two over 10. From there, we could multiply one-fourth by two-tenths. And then we could simplify. Both two and four are divisible by two. We multiply the numerators together to get one times one and the denominators together to get two times 10, which is 20. This is telling us that 25 percent of 0.2 is one twentieth.

But since we want this final answer as a decimal number, we could rewrite this fraction with the denominator of 100. 20 times five is 100. If we multiply the denominator by five, we need to multiply the numerator by five. One twentieth equals five hundredths. And that means to write it as a decimal, we put a five in the hundredths place. Five hundredths as a fraction written as a decimal is 0.05.

I know we said we’re gonna look at two examples, but let’s just see one more. Let’s say you got to this point: one-fourth times 0.2. Multiplying 0.2 by one-fourth would be equal to 0.2 divided by four. And if we divide 0.2 by four, we bring up the decimal. Four goes into two zero times, but four goes into 20 five times with no remainder. And that means 0.2 divided by four is 0.05. It’s 0.05. There are lots of ways to calculate this. Just remember to follow the instructions and give your final answer as a decimal number, as indicated here.

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