Question 102760
"If 5 to the 21st power * 4 to the 11th power = 2 * 10 to the nth power, what is the value of n?"
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[5^21]*[4^11] = 2*10^n

10^n = [5^21 * 4^11]/2

Take the log of both sides to get:

n = 21log5 + 11log4 - log2

The answer I get is 22.073

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You would not want to calculate this without a calculator.
I think you may have made a mistake in your posting.
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Cheers,
Stan H.