2:4+5:3

Interpret colon as division: 2:4 = 2/4 = 1/2, and 5:3 = 5/3.

Then sum: 1/2 + 5/3 = (3 + 10)/6 = 13/6.

So, 2:4 + 5:3 = 13/6 = 2 1/6 ≈ 2.1667.