Ratio 1:2:3 means we have x, 2x and 3x as the three parts
x+2x+3x = 42
6x = 42
6x/6 = 42/6
x = 7
Since x = 7, this means 2x = 2*7 = 14 and 3x = 3*7 = 21
Dividing 42 into the ratio of 1:2:3 means we have 7:14:21 as the answer
If we divide all three parts of 7:14:21 by the GCF 7, we reduce it down to 1:2:3
As a check,
7+14+21 = 21+21 = 42
so it works out