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ellisje22
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ellisje22
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Thanks everyone! I understand it now. I guess I hadn't thought we'd have to do very many power to the power of a power type of questions on the real gmats so I wasn't very practiced at exponent questions.
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srinivasssrk
Yes, I agree with the previous solution. Another way to look at the problem is...

Instead of solving the whole problem, you can also note that on the right hand side, the only factors of 10 are 2 and 5. Hence, on the right hand side, the maximum power of 5 is n (because there are no other multiple of 5 on the right hand side). Now, equating n = the power of 5 on the left hand side, you get n = 21.

-Srinivas (mathguru).



Please can you show it us in detail, it's an interesting approach
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ellisje22
This was the very first question in my GMATPrep software. I had no idea how to approach it which is scary for your first problem. Could someone please tell me how to approach this problem and walk me through steps to solve it?

(5^21)(4^11)=2(10^n)

What is the value of n?

PS - The answer is 21


(5^21)(4^11) = (5^21)(2^22) = 2(10^n)
(2^21)(5^21) = 10 ^ n
= 10^21 = 10 ^n
=> n = 21
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allabout
srinivasssrk
Yes, I agree with the previous solution. Another way to look at the problem is...

Instead of solving the whole problem, you can also note that on the right hand side, the only factors of 10 are 2 and 5. Hence, on the right hand side, the maximum power of 5 is n (because there are no other multiple of 5 on the right hand side). Now, equating n = the power of 5 on the left hand side, you get n = 21.

-Srinivas (mathguru).


Please can you show it us in detail, it's an interesting approach


I think he already made it too clear: since LHS contains 5^21 and 5 is a prime --> RHS must contain EXACTLY 5^21 ...whereas, the highest power of 5 in RHS is 5^n ----> n must be 21.



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