Xiao Ming investigated the daily weather conditions in the area in April and made statistics

1. 30 days. The number of days in April in the Gregorian calendar is fixed and has nothing to do with the weather.

2. The number of sunny days accounts for 40% of the total number of days. Suppose the proportion of sunny days to the total number of days is x, and the proportion of rainy days to the total number of days is a. Then according to (1), a=20 %+10%=30%

Then x= 100%-20%-10%-a=100%-20%-10%-(20%+10%)=40%