Write the expression for a number used as a factor fifteen times being multiplied by a number used as a factor ten times. then, write the product as one power.

This is exponents so a number used as a factor fifteen times is X^15. Then multiplied by a number used as a factor ten times is X^10. 

The answer is: X^15 * X^10 = X^25

PS: You don't multiply exponents, you add them.

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Two because two of one thing is two.