Explain how using basic facts can you find 10 x 20 x 30 x 40 mentally?

Take the left side of each number first. Do 1 x 2 x 3 x 4. That equals 24. Easy. Now, count the 0's in the equation which are 4 of them. Add the four zeros and to the 24 and that's your answer. 240,000

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