How to calculate logrithm of base of any number in fx-991ms

The NEWYES NY-991MS and CTIFREE fx-991ES PLUS calculators do not have a dedicated "FACT" button like the Casio FX-83GTX. However, you can still find prime numbers on these calculators.
To find prime numbers:
NEWYES NY-991MS:
Press the "MODE" button.
Choose "PRIME" from the list of options.
Enter the desired number and press "=" to check if it's prime.
CTIFREE fx-991ES PLUS:
Press the "MODE" button.
Select "TABLE" or "TABLESET."
Input a starting point and an ending point, then observe the table for prime numbers.
Although the techniques may vary from those used on the Casio FX-83GTX, they prove to be effective for prime number calculations on the designated calculators.

PDF]fx-570MS/991MS Additional Functions - Support - Casio

support.casio.com/pdf/004/fx570MS_991MS_E.pdf

Casiodisplay format (Disp) settings while the calculator is in the BASE ... Be sure to checkthe current calculation mode (SD, REG,. COMP ... Use [ and ] to display the expression 4 + 4. Press A ... want to perform scientific function calculations. COMP .

The Casio fx-991es, fx-570es and - Numericana

www.numericana.com/answer/casio.htm

The Casio fx-991ex succeeds the fx-991es (functionally identical to the ... Both are nonprogrammable nongraphing scientific calculators, with natural ... Side-by-side comparison of the fx-991EX and fx-991ES PLUS. ... Displays QR codes for smartphone use .... Work out a formula for many values of the input variables.

CASIO fx-991MS Calculator Tutorial: Lesson 5- Dealing with ...

I checked in the manual and found that this calculator does not support Base-N calculations. On the FX-991ES Plus, which has a Base-N mode, fractions , exponents, and other floating points are not supported. The non-integer part is chopped off.

On a fx-991MS? With many other models, including the fx-991ES, I'd say you have the calculator in binary mode but the 991MS doesn't have such a mode.

Press MODE 4 to enter the BASE-N mode. Select the input base. Enter the number. Press =. Select the output base and see the result.

Your calculator knows only the decimal logarithms log or log_10 and the natural logarithms (ln or log in base e).
So you cannot compute directly the logarithms in any bases other than 10 and e.
A workaround consists in using the relation
log in base b of a number a (log_b (a))
log_b(a)= (log_10(a) ) / (log_10 (b))
or the relation
log_b(a)= ln(a)/ln(b)

log_2(0.3)=log(0.3)/log(2) where log is log in base 10
Similarly
log_2(0.3)=ln(0.3)/ln(2)
As to the multiplicative factor you had at the beginning of your expression, just multiply the value obtained by one on the formulas above (both formulas will give the same result) by 0.3

how to solve probability in fx-991ms

Hello, There is a key for that, the one labeled [ln] for natural logarithm. For log in base 10 use the key [LOG] [LN] 10 [ENTER] gives 2.302585093. As you certainly know, you cannot take the logarithm of a negative number, nor of Zero.
Hope it helps.

there is one button ab/c beneath CALC... if u want to calculate 7 mod 4 then... u should press 7 then ab/c 4 and equal to
1, 3 ,4 which is 4*1=4 and 7-4=3 remainder...

In any scientific calculator log2(n) can be  calculated with either ln or log function as follows
 
Log2(n)= ln(n) / ln(2)
 
Or
Log2(n)=log(n) / log(2)

both will give nearly the same answers