Given functions are


The total number of ducks and swans in the lake after n months can be determined by adding the functions s(n) and d(n).





Taking 2 as common, we get

Hence The total number of ducks and swans in the lake after n months is
For the first digit you have 10 options (0..9).
For each next digit you can't choose the same digit, so you have 9 options.
So number of combinations is 10*9*9*9*9 = <span>65610</span>
0.73+0.68+0.88+0.74+0.81=3.84
3.84 divided by 5
=0.768x100
=76.8% or 77%