GMATPrepNow
If \(3^k\) = 16, and \(2^j\) = 27, then kj =
A) 8
B) 9
C) 10
D) 12
D) 15
* Kudos for all correct solutions
Another approach is to
isolate the 3 in both equations. Here’s what I mean:
Given: 3^k = 16
Rewrite 16 as 2^4 to get: 3^k = 2^4
Raise both sides to the power of 1/k to get: (3^k)^(1/k) = (2^4)^(1/k)
Use power of power law to simplify:
3 = 2^(4/k)Given: 2^j = 27
Rewrite 27 as 3^3 to get: 2^j = 3^3
Raise both sides to the power of 1/3 to get: (2^j)^(1/3) = (3^3) ^(1/3)
Use power of power law to simplify:
2^(j/3) = 3We now have two equations:
3 = 2^(4/k)2^(j/3) = 3Since both equations are set equal to 3, we can write:
2^(4/k) =
2^(j/3)Since the bases both equal 2, we can conclude that 4/k = j/3
Cross multiply to get: jk = (4)(3)
So, jk = 12
Answer: [spoiler]D[/spoiler]
Cheers,
Brent