Working backwards is a strategy used to solve a problem in which you are given the answer and asked to find an unknown piece of information.

The sequence of actions starts with the problem solution and ends with the problem statement.

QUESTION: Lori is given a collection of comics. She buys seven new ones, then gives one-half of her resulting collection to her friend and then has eight comics left. How many comics were originally in her collection?

The following is a list of operations with the final result.

• Lori is given a collection of comics
• She adds seven new comics to the collection
• She gives one-half of her resulting collection to her friend
• She has eight comic books left.

In using this stategy to solve this problem, start with the end result - eight comics left, reverse the order in which the operations are given and do the opposite of each operation.

• Lori has eight comic books left.
• She doubles her collection by getting some comic books from her friend (double 8 to obtain 16)
• She takes away seven new comics from the collection (16 - 7 = 9)
• Lori has the original number of comic books she started with (9).

SOLUTION: Lori started with nine comic books in her collection.