C. 60: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60 1,000: 1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500, 1000 Now we find the common numbers. One doesn’t count as when multiplied later on, it will not change anything. 60: 2, 4, 5, 10, 20 1,000: 2, 4, 5, 10, 20 The highest common factor is 20 because it’s, well, the highest number. D. Do the same thing for D. 24: 1, 2, 3, 4, 6, 8, 12, 24 880: 1, 2, 4, 5, 8, 10, 11, 16, 20, 22, 40, 44, 55, 80, 88, 110, 176, 220, 440, 880 20 and 880: 2, 4, 8 8 is the Highest Common Factor. E. Do the same thing with E. 90: 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90 1,000: 1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500, 1000 90 and 1000: 2, 5, 10 10 is the Highest Common Factor.