Each boy and girl is advised to bring a bottle of water. (each boy/girl)
However, when each modifies only one of the subjects joined by and, plural verb follows.
Each boy and his friend are allowed to enter the exhibition. (each boy+his friend)
(In this case you could divide the two nouns in the subject to mean unique things and use a plural verb.)Law and order is government's first priority.
Gin and tonic is a popular drink among sailors.
Bed and Breakfast seems the cheapest kind of accommodation in Britain.
The secretary and financial controller, Mr. Lee Wai Tak, has decided to resign.
(In this case, one person, Mr. Lee Wai Tak, is holding the two positions of secretary and financial controller.)All I want is a few good friends.
All was not well in the neighbouring country.
Fifteen minus five equals ten.
Three multiplied by three is nine.
Statistics don't always show the real picture. Data can be misleading.