Then borrow 2/7, that is, the number of books borrowed is 49x2/7= 14.

Then the remaining number of books is 49- 14=35.

That is, the number of books left is 35.

Subtraction operation property

Subtracting the sum of two numbers from a number is equivalent to subtracting each addend in the sum from this number in turn. For example:134-(34+63) =134-34-63 = 37.

A number minus the difference between two numbers is equal to this number minus the minuend in the difference, and then the subtraction. For example: 100-(32-15) =100-32+15 = 68+15 = 83.