GMAT Practice Paper 1 n0. 1

5*4^11=2*10^n
i.e. 5*2^22 = 2*10^n
i.e. 10*2^21 = 2*10^n
i.e. 10*2^20 = 10^n
i.e. 2^20 = 10^(n-1)
approx 10^6 = 10^(n-1)
approx 5

let me know...

Thank you so much!

thank you so much Suyog

I am sorry Suyog, the answer should be 21. I thanked you before I had reviewed your answer

can you confirm the second expression...
it is..2*10^n or 2^n*10
let me know...

Hello Mimi,
If this question is from the GMAT Testprep then you have posted it wrongly.


Its actually 5^21*4^11=2*10^n and the answer would be as follows


5^21*4^11=2*10^n

5^11*5^10*4^11=2*10^n

20^11*5^10=2*10^n

20^10*20^1*5^10=2*10^n

100^10*20^1=2*10^n

10^20*2*10=2*10^n ( Because 100 is 10^2 and 20 is 2*10)

10^21*2=2*10^n and therefore n is 21

Hope I am clear Mimi!!

I guess this is a much simpler way to look at it...

5^21*4^11 = 2*10^n

5^21*2^22 = 2*2^n*5^n
5^21*2^21*2 = 5^n*2^n*2

hence, n = 21

I hope you guys understand!

Cheers!

thanks guys....I understsand both concepts

Are we trying to get all the values to the same base or so that we can equate the powers? For example, in moneyman's response ..

5^21*4^11=2*10^n becomes 5^11*5^10*4^11=2*10^n

AND

20^11*5^10=2*10^n becomes 20^10*20^1*5^10=2*10^n

Why not 20^8 * 20^3, for instance? I'm guessing because then we couldn't do the 20^10 * 5^10 to get 100^10 calculation.

Seems to be random. Are there any guiding principles when answering these questions?