The total time required to burn a single DVD is eighteen minutes.
Last weekend, Jason spent ninety minutes burning DVDs. Write a multiplication equation to
determine the number of DVDs that Jason burned, and then solve it.
First off, let’s define a variable. Let 𝑥 be the number of DVDs that
Jason burned last weekend. So he burned 𝑥 DVDs, and each one of them took eighteen minutes to
burn. And in total, he spent ninety minutes burning those DVDs. So we can say 𝑥 times eighteen, the number of DVDs times the
number of minutes per DVD, equals ninety.
Now if we’re writing an algebraic equation, we wouldn’t normally leave that as
𝑥 times eighteen. We’d write it as eighteen 𝑥. Means the same thing, eighteen times 𝑥 or 𝑥 times
eighteen, but it’s just a slightly more sophisticated algebra.
Well that’s the first part the question done then. We’ve written a multiplication
equation to determine the number of DVDs, so now we’ve gotta go ahead and solve it. So eighteen times 𝑥 is equal to ninety. Well I want to know what
𝑥 is. Now the opposite of multiplying by eighteen is dividing by eighteen. So if I divide the left-hand side by eighteen, I’ve got 𝑥 times eighteen
divided by eighteen. The eighteens are going to cancel, so I’m just gonna be left with
But the problem is I’ve just broken my equation; I’ve divided the left-hand side
by eighteen but I didn’t divide the right-hand side by eighteen. So I need to do that; I need to
divide the right-hand side by eighteen as well. Now, they’re equal. All we have to do now is divide ninety by eighteen or work out
what do I need to multiply eighteen by to get ninety.
Well I know that five times ten is fifty and five times eight
is forty, so five times eighteen is fifty plus forty; that’s ninety. So the
answer is five. And answering the specific question how many DVDs did Jason burn, the answer was