# Thread: Logarithm Help

1. ## Logarithm Help

A, B, and D worked out, but when I try to do C I run into a problem.

I use the formula:
f(t)=90-15log(6+1)

For an answer I get:
90+log(1/474561509943)

Im pretty sure im doing something wrong because the other answers were more like 90 and 50

2. Originally Posted by whiteforlife

A, B, and D worked out, but when I try to do C I run into a problem.

I use the formula:
f(t)=90-15log(6+1)

For an answer I get:
90+log(1/474561509943)

Im pretty sure im doing something wrong because the other answers were more like 90 and 50
When I did 90-15log(7) I got an answer of 77.3 (3sf). Are you sure you put it in your calculator correctly?

3. That was it. I did it in my calculator wrong 3 times. Thanks for catching my stupid mistake. Also for part E, would about 6 months be a correct answer or is it supposed to be exact?

4. Originally Posted by whiteforlife
That was it. I did it in my calculator wrong 3 times. Thanks for catching my stupid mistake. Also for part E, would about 6 months be a correct answer or is it supposed to be exact?
I got an answer of 9 (I assume t is in months)

$75 = 90 - 15log_{10}(t+1)$

$75-90 = -15log_{10}(t+1)$

$-15 = -15log_{10}(t+1)$

-15 will cancel to give us $log_{10}(t+1) = 1$

$t+1 = 10^1 = 10$

$t=9$