1 : 2.5 is the constant proportionality.
1 (× 2) : 2.5 (× 2) = 2 : 5
1 (× 4) : 2.5 (× 4) = 4 : 10
1 (× 6) : 2.5 (× 6) = 6 : 15
1 (× 8) : 2.5 (× 8) = 8 : 20
4.5m questions
5.9m answers