He's wrong! It's 6, not 9.
Max is painting 3 wooden toys ( wooden airplane, car,
and train). He can choose red, yellow or green. Each
toy must be painted with a different paint. How many
different ways can Max paint the cars?
He can choose the color to paint the airplane in 3 ways.
For each of those 3 ways he can choose a color to paint
the airplane, there remain 2 ways he can choose a color
to paint the car.
That's 3*2 or 6 ways to paint the airplane and
the car.
For each of the 3*2 or 6 ways to paint the airplane and
the car, there remains only 1 color he can choose to
paint the train.
So that's 3*2*1 or 6*1 = 6 ways to paint all three toys.
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As a check:
1. Paint the airplane red, the car yellow, the train green.
2. Paint the airplane red, the car green, the train yellow.
3. Paint the airplane yellow, the car red, the train green.
4. Paint the airplane yellow, the car green, the train red.
5. Paint the airplane green, the car red, the train yellow.
6. Paint the airplane green, the car yellow, the train red.
That's all the possible ways, and there are 6 of them, so
the answer 6 is correct.
Edwin