Answer :

AlgebraicAardvark

Let J be the number of CDs Jake has.

 

Ben has four more than twice as many as Jake.

"four more than" mean "+4"

"twice as many as Jake" means "2J"

So "four more than twice as many as Jake" means "2J+4".

 

If they have a total of 31, we can add J and 2J+4 and set it equal to 31:

       J + 2J+4 = 31

           3J + 4 = 31

      3J + 4 - 4 = 31 - 4

                 3J = 27

                   J = 9

Jake has 9 CDs.

regalmocha17

Jake has 9 CDs.

Ben has four more than twice as many CDs as Jake can be denoted as:

2J + 4 = B

J + B = 31

Replace B with 2J + 4 to solve for J.

J + 2J + 4 = 31

3J + 4 = 31

3J = 31 - 4

3J = 27

J = 27/3

J = 9

Therefore, Jake has 9 CDs while Ben has 22 CDs.