A simple annoying question

We have been arguing over the following question that is in a relatively easy paper:

'The weather during Ratty's holiday was strange.
It rained on 15 different days, but it never rained for a whole day. Some days it did not rail at all.

After a rainy morning there was always a clear afternoon.
Before a rainy afternoon there was always a clear morning.
There were 12 clear mornings and 13 clear afternoons in all.

How long was Ratty's holiday altogether?

I worked out 27 1/2 days by adding up all the mornings and afternoons of clear days then added 15. However this is wrong as parts of the clear mornings are involved in the rainy days.

My Brother is sure the answer is 25 and will not accept any others. He has no real proof though.

Finally my Dad thinks it is 20 : 15 different rainy days : Let's say 8 rainy mornings and 7 rainy afternoons. That makes 8 less clear afternoons and 7 less clear mornings: 5 clear afternons, 5 clear mornings, which pair together to make 5 days which is added onto the 15 rainy days.

The answer is probably obvious ; I know it is very easy compared to these other threads. :blush:

but all help is greatly appreciated