The ratio of ducks to chickens in our backyard is 2:3. The total number of ducks and chickens together is 30. If mother gave away 3 chickens to our neighbor, what is the new ratio of ducks to chickens now? ​

2+3=5
30 divide by 5 is 6
6*2 is 12 6*3=18
Ducks=2 Chickens=3
Ducks also equal=12 Chickens also equal= 18
18-3=15
12:15
Simplify:
4:5

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.