1200=250(1+x/12)^4.2 how do you find x?

You can do it that way but you do not need to use logs because there is no unknown inidice.

 

This is how I would do it :)

 

1200=250(1+x/12)^4.2

 

\(1200=250(1+x/12)^{4.2}\\ 4.8=(1+x/12)^{4.2}\\ 4.8^{1/4.2}=[(1+x/12)^{4.2}]^{1/4.2}\\ 4.8^{1/4.2}=1+x/12\\ 4.8^{1/4.2}\;-1=x/12\\ 12[4.8^{1/4.2}\;-1]=x\\ x=12*[4.8^{1/4.2}-1] \)

 

x= 5.433377751

1200=250(1+x/12)^4.2 how do you find x?

 

Let (1+x/12)=n, substitute,

1200=250 X n^4.2, divide both sides by 250,

4.8=n^4.2, take the log of 4.8

0.68124=4.2 X n divide both sides by 4.2

n=.1622, this is the log of base 10

n=10^.1622

n=1.452780, but n=(1+x/12), so we have:

1.452780=1+x/12, subtract 1 from both sides,

.452780=x/12, multiply both sides by 12

x=5.4334