Lately I have been challenging myself to solve 6x6 puzzles without using scratch paper for factoring or other figuring. Below is a link to a file folder full of the puzzles I have solved in this way, and using deductive logic alone without recourse to trial and error.
Some helpful things to remember:
1. The numbers in each row and column must add up to 21.
2. Numbers divisible by 5 all end in 0 or 5.
3. Numbers divisible by 3 all have digits that add up to a multiple of 3. For example, take 24: the digits 2 and 4 add up to 6 which is a multiple of 3. This fact comes in handy for quickly determining factors for larger numbers.
Here is the link to a set of puzzles you can print out and solve:
