Which is the simplest form of 42:12:72?

To find the simplest form of a ratio, each part of the ratio should divided by their largest common factor.

42 can be divided by: 1, 2, 3, 6, 7, 14, 21, 42

12 can be divided by: 1, 2, 3, 4, 6, 12

72 can be divided by: 1, 2, 3, 4, 6, 12, 24, 36, 72

So, their largest common factor is 6. Then,

42:12:72 = (42 ÷ 6) : (12 ÷ 6) : (72 ÷ 6) = 7:2:12