IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry - HOw can i take the value of log without see the log tabels for comptition. exams

bvsatyaram

U are expected to at least remember logarithms of 2 and 3.
Log 10 is 1.
Express the number in terms of 2,3 and 10. (Most of the cases this works.)
Suppose we need to find log 75,
then we do as follows:
75=3*25=3*10*10/(2*2)
So,
log 75 = log3 + 2log10 - 2log2.

Another case could be approximating log.
Consider an MCQ with any pair of its options differ by atleast 1.
Say, the options are a) 5.62 b) 3.2 c) 7.9 d) 21.4
How approximate the nu,ber to nearest power of 10. Suppose, you need to find log (621453), 621453 is between 100000 and 1000000.
So, log (621453) must lie bet 5 and 6.
So, option A.

If neither of the above 2 cases is true, then definitely, logarithms will be given. If not, beleive me, the question will be deleted for evaluation.

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