# Logs!?

Hey all!

Does anyone know a website that shows one how to do quick and easy log calculations in their head??

Hi Julio

I don’t know any site, but I can share what I know, although it may not really help you.

1. Know that log that you need to calculate are often given on the MCAT.

2. It is useful to know the properties of logs (i.e. log(a/b) = log a - log b)

3. obvious but log 1 = 0

4. if you end up calculating log of a negative number you messed up, because it is not defined (at least with real numbers)

5. a quick way to estimate the log of a number: often times, you can get away with knowing a range rather than the exact value (remember, MCAT is a multiple choice test). Say you have to estimate log (543). You simply figure out that 543 is between 100 and 1000 (you take the prior and next powers of 10). So log(543) is between the log of these same numbers. So you can easily say that log of 543 is between 2 (or log 100) and 3 (or log 1000). Look up the answer and pick it.

6. Now if they are very vicious and for the above calculation they throw two choices like 2.4 or 2.7. Both are between 2 and 3 and that doesn’t help. A quick way to figure it out here is the following: 543 is about midway between 100 and 1000, so you’d think the log is midway between 2 and 3. Well I am not sure how to explain it, but on the log scale you progress faster toward the next unit compared to the decimal scale:

log 500 is more than 2.5

log 600 is more than 2.6

log 900 is more than 2.9

Of course that may not be enough, but with practice it becomes easier.

Similarly log(8745) well quickly you see that the number is between 1000 and 10,000 so the log is between 3 and 4, closer to 4 and more more than 3.8 ( with experience you will even say more than 3.9). But I believe that if you can narrow it between 3.8 and 4 then that’s not bad at all - what do you think?

Not sure I helped at all. I just hope I didn’t confuse.

Wow, redo! That was a great explanation. I went in with just that amount MINUS figuring the log of 500 was more than 3.5, and usually the answer was obviously there.

Thx Kate

I guess there might be many ways to figure it out, but back to Julio, whichever way you chose, make sure you practice. If you can estimate 20 or 40 logs within 0.5 then you are set for the MCAT. You can use excel it has a random number generator to quickly make as many numbers as you want and try to estimate the log (and compare it to the actual log). If you want a spreadsheet I can get that for you.

I also forgot to mention the log of small numbers (numbers smaller than 1) will end being negative. It works the same way, but it is a bit more difficult. So instead of explaining, try and see how it works.

Good luck.

Redo:

Excellent explanation. Concise and to the point. Maybe you should consider teaching MCAT on the side during med school.

Thx Apple. I will be teaching but not for the MCAT. I wonder what the pay is for MCAT instructors…

Redo, How much do you plan on teaching? I have been going back and forth trying to decide if I can still teach on the side during med school. I don’t want to compromise my grades or opportunities, but it sure would be nice to keep earning something.

Hi Insects. So far I am set for about 10-12 hr/week bringing in about 1600/month.

The first semester at my school is Pass/Fail, so that gives the time to experiment. Given the amount of debt I am going to pile up, I am trying to see what I can do on the side for the first year, and perhaps the second. But I do not plan on teaching much third and fourth years.

I do not know if it is reasonable. Some say it’s OK, others say don’t. I believe I can make it on the money I am allowed to borrow. However, @ 7%, borrowing will be expensive.

My plan is to work and pay for at least 1 full year tuition/living expense out of 4 years. We’ll see.

I agree about not teaching the 3rd and 4th years. That would be impractical. For me the decision to teach for the first two years depends in part on where I am accepted and what the schedule will be. If I end up with a two-hour commute, it won’t work. I’ll just have to see. Thanks for your opinion!