Those are the "factors" of 80. They are: 1, 2, 4, 5, 8, 10, 16, 20, 40, and 80.
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The highest common factor is the greatest number which both numbers can divide by evenly. In this case, the greatest number 40 can divide by is 40. 80 can also divide by 40, and so this is a common factor. As no numbers greater than 40 will be able to divide 40 evenly, the hcf of 40 and 80 is 40.
1, 2, 4, 5, 10, and 20 divide evenly into 20.
1 and 13
5 & 17
1 2 7 14 49 and 98 all divide into 98 evenly.