By looking at the number line, you can see how far 100 and 1000 are away from each other ... Next, count the number of intervals. There are 10 in total. How many 10s go into 50?

Can you see the link between pairs that make 10 and pairs that make 100? A number line can help you find more tricky number pairs to 100. For example, here is the number line with the number 63 ...