Frank goes to the store to buy some hot dogs and hot dog buns for a cookout. He is surprised to find that hot dogs are sold in packages of eight, and buns are sold in packages of 10. Frank doesn't want to have more hot dogs than buns, or more buns than hot dogs. How can he make sure he buys the same number of both?
In this example, Frank would need to find a common number for 8 and 10. A common number is a number that is a multiple of two lesser (smaller) numbers.
One way to find a common number is to create number lines. In a number line, you start with a certain number and then keep adding by that number. For example, a number line for 3 would look like this:
---3---6---9---12--->
Using number lines is a good way to see the multiples of a number. In this case, we see that the multiples of 3 are 6, 9, 12, and so on.
Frank could use number lines to find the common number of 8 and 10.
---8---16---24---32---40--->
----10----20----30----40--->
The first common number is 40. This is how many hot dogs and buns Frank should buy.
But what if you're not able to use number lines? After all, you might not always have a piece of paper on hand. That's all right; there's another way to find common numbers.
The best way to do it is to start counting by the greatest (larger) number. In the example, Frank would start counting by 10 and find the first number that he would reach counting by 8. If he counts correctly, he'll find that the first common number is 40.
