(5^11) . 4^10 = 2 . 10^n ….. n is between which 2 integers?
OA 13 and 14
(5^11) . 4^10 = 2 . 10^n
This topic has expert replies
-
- Junior | Next Rank: 30 Posts
- Posts: 20
- Joined: Mon Apr 27, 2009 6:15 pm
- Thanked: 1 times
- GMAT Score:650
Last edited by keizer Soze on Sun May 03, 2009 11:40 am, edited 2 times in total.
-
- Legendary Member
- Posts: 1035
- Joined: Wed Aug 27, 2008 10:56 pm
- Thanked: 104 times
- Followed by:1 members
(5^11) . (4^20) = 2 . (10^n)
=>(5^11)*(2^2)^20=2*(2*5)^n
=>(5^11)*(2)^40=[2^(n+1)]*5^n
equating the bases on both sides
we get 2 values of n
n=11; n+1=40=>n=39. which is weird.
is there any typo in the question?
=>(5^11)*(2^2)^20=2*(2*5)^n
=>(5^11)*(2)^40=[2^(n+1)]*5^n
equating the bases on both sides
we get 2 values of n
n=11; n+1=40=>n=39. which is weird.
is there any typo in the question?
-
- Junior | Next Rank: 30 Posts
- Posts: 20
- Joined: Mon Apr 27, 2009 6:15 pm
- Thanked: 1 times
- GMAT Score:650
I solved it this way:
5^11 . 4^10 = 2 . 10^n
5^11 . 2^19 = 10^n
10^11 . 2^8 = 10^n
10^11 . 2^8 . 5^8/5^8 = 10^n
10^19 . 1/5^8 = 10^n (A)
Here: 5^8= 10^8 . 1/2^8 (B)
2^10=~ 10^3............ so, 2^8 =~ 10^2,4
Again in (B): 5^8 = 10^8 / 10^2,4 = 10^5,6
Finally in (A): 10^19 / 10^5,6 =~ 10^n
10^13,4 =~ 10^n
n=~ 13,4
I think that this steps are Ok....
5^11 . 4^10 = 2 . 10^n
5^11 . 2^19 = 10^n
10^11 . 2^8 = 10^n
10^11 . 2^8 . 5^8/5^8 = 10^n
10^19 . 1/5^8 = 10^n (A)
Here: 5^8= 10^8 . 1/2^8 (B)
2^10=~ 10^3............ so, 2^8 =~ 10^2,4
Again in (B): 5^8 = 10^8 / 10^2,4 = 10^5,6
Finally in (A): 10^19 / 10^5,6 =~ 10^n
10^13,4 =~ 10^n
n=~ 13,4
I think that this steps are Ok....
-
- Junior | Next Rank: 30 Posts
- Posts: 20
- Joined: Mon Apr 27, 2009 6:15 pm
- Thanked: 1 times
- GMAT Score:650
i solved in the following way.
5^11 . 4^10 = 2 . 10^n
LHS goes..
5^11 . 2^20
2* (5^11*2^19)
2* (5^11*2^11) * 2^8
2* (10^11) * 2^8 -------I
now 2^8 =256
thus more than 10^2 but less than 10^3
thus we may consider 10^2 <2^8 < 10^3
thus n is between 10^11*10^2 and 10^11*10^3 ie 13 < n <14
hope this helps
5^11 . 4^10 = 2 . 10^n
LHS goes..
5^11 . 2^20
2* (5^11*2^19)
2* (5^11*2^11) * 2^8
2* (10^11) * 2^8 -------I
now 2^8 =256
thus more than 10^2 but less than 10^3
thus we may consider 10^2 <2^8 < 10^3
thus n is between 10^11*10^2 and 10^11*10^3 ie 13 < n <14
hope this helps