采蘑菇，晴天采了17个，雨天采了8个，***采了84个，平均每天采14个，问雨天才多少个

晴天=x天

雨天=y天

采蘑菇，晴天采了17个，雨天采了8个，***采了84个

17x+8y=84 (1)

平均每天采14个

(17x+8y)/(x+y)=14

17x+8y=14x+14y

x=2y (2)

sub (2) into (1)

34y+8y=84

y=2

from (2)

x=4

雨天采多少个

=2(8)

=16个