To solve a Yohaku, you must fill in the blank space so that the cells give the sum or the product shown in each row and column.

Some yohakus have no further restrictions. These puzzles have an infinite number of solutions!

Most Yohakus, though, have a restriction (written below the puzzle) that needs to be satisfied. These will require a bit more thought to solve.

Looking carefully at the sum or product in each row or column will give you some clues as to how these values can be decomposed and, combined with information from other rows and columns, will help you find the values for certain cells.

For example, in this 3-by-3 Yohaku, the restriction is ‘Use prime numbers’. Looking at the top row, you need to think of three prime numbers that multiply to give 8. There is only one way to do this i.e. 2×2×2. Putting these in, we can now look at the left-hand column for further clues: what values could we use so that 2 times a prime times a prime gives 50?

Again, there is only one way of doing this as shown below on the right. With a little more thought, it should be possible to fill in the remaining cells.

**SOLUTION**