Plus or Minus is a puzzle to help children master the  
skills of addition and subtraction.  Numbers are
arranged in a 5 x 5 grid.  The columns add up to
the answers at the bottom, and the rows add up to
the answers on the right.  The bottom row, the
right-hand column, and the diagonal all add up to the
answer in the bottom right-hand corner, which is left
blank.  Children must place a plus or a minus sign in
front of each number to make sure everything adds up
correctly.  There are three books of sixty puzzles each.

Price: $5.95  To buy on Amazon, click
The puzzles exist as Kindle ebooks, but work better as
Math Puzzle Books