Multiply a Decimal by a Decimal Math with Mr J

Welcome to Math with Mr. In this video, I'm going to cover how to multiply decimal by decimal. So, let's jump right into number one where we have 72 hundredths * 4 tenths. Now, the three steps that we're going to take in order to solve these correctly are at the top of your screen. And step one, we remove or forget about any decimals and we rewrite the problem. So, we can rewrite it as 72 * 4. Now, these decimals will come back into play later in the problem. Step two, we multiply just like we would any other whole numbers. So, 72 * 4 here, 4 * 2 is 8. And then 4 * 7 is 28. And we get 288 there. That brings us to step three where we need to place the decimal correctly in our answer. So, we go back up to our original problem and see how many digits are to the right or are behind decimal, however you want to think of it. So, we have this seven here, this is one, two, and three. like circling them, that way don't forget anything. So, that seven, the two, and the four are all to the right of decimal. That means our answer needs to have three digits to the right or behind the decimal. So, we can do one of two things. With whole number, the decimal comes at the end here and we can think of it like this, moving it in one, two, three, and placing the decimal here and we get an answer of thousandths, which is correct. Or we can take look at I'm going to rewrite 288 here. We have one, two, three digits behind the decimal and we can just place the decimal there. So, couple different ways of thinking of placing that decimal correctly, they both will give you the same answer. So, our final answer is 288 thousandths. On to number two, where we have 6 and 3/10 * 2 and 9/10. So, first step, remove and forget about any decimals, and we end up with 63 * 29. Now, we multiply. 9 * 3 is 27. 9 * 6 is 54 + 2 is 56. Done with the nine, done with the two. We're going place to the left here, so we need our zero as we work our way over to the two. 2 * 3 is 6. 2 * 6 is 12. So, now we add our partial products together. 7 + 0 is 7. 6 + 6 is 12. 1 + 5 is 6 + 2 is 8. And we have our one over here. So, we get 1,827. So, we need to place our decimal correctly now. Take look at the original problem, and we have one two digits behind or to the right of decimal. That means our answer needs to have the same thing, two digits behind the decimal. So, we have one, two, and we can place our decimal here. So, our final answer is 18 and 27 hundredths. So, there you have it. There's how you multiply decimal by decimal. hope that helped. Thanks so much for watching. Until next time, peace. Mhm.