Ernest is planting flowers, four to a row. He is planting red, purple, yellow,
and white flowers, Each row must contain all four colors and be in a different
order from right to left. How many rows can Ernest plant?

For any row, he can choose the leftmost color of flower to plant in any of 4
ways.

For each of those 4 ways he has chosen a color for the leftmost color of
flower, there remain only 3 colors of flowers left to plant just right of the
leftmost flower.

So that 4*3 ways he can plant the leftmost and the next to left most.

For each of those 4*3 ways he has chosen 2 colors for the two leftmost flowers,
there remain only 2 colors of flowers left to plant next to the rightmost
flower.

So that 4*3*2 ways he can plant the three flowers on the left.

For each of those 4*3*2 ways he has chosen 3 colors for the three leftmost
flowers, there remain only 1 color of flower left to plant on the far right.
flower.

So that's 4*3*2*1 or 24 different arrangements for a row of flowers. So
he can plant 24 rows.

Edwin