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

Price: $5.95.

To buy on Amazon, click
The puzzles exist as Kindle ebooks, but work better
as paperbacks.
Math Puzzles: Plus or Minus