Analysis: It is known that 100 people borrow books from the library, 35 people borrow both books and 85 people borrow story books. According to the known conditions, the formula is as follows:

35+( 100-85)

=35+ 15

=50 people

Fifty people borrowed science books.

definition

Addition: the operation of combining two numbers into one number.

Subtraction: when two addends and one of them are known, the operation of finding the other addend.

Multiplication: the operation of finding the product of two numbers.

Division: the operation of finding another factor by knowing the product of two factors and one of them.