Answer: A. 
Step-by-step explanation:
Total digits on keypad = 5
According to permutation,
If repetition of digits is not allowed then the number of 5-digits passwords can be formed = 5!
= 5 x 4 x 3 x 2 x 1 [n!=n x (n-1) x (n-2)x ... x 1]
=120
The probability that someone guesses the correct code = 
Hence, the correct option is A.
ANSWER
x=100,y=10
EXPLANATION
The given logarithmic equations are;
This implies that,
and
This implies that,
Put equation (2) into equation (1)
Hence y=10.
This implies
Sina - (cosa)(tanb)/cosa + (sina)(tanb)
sina ≡ (tana)(cosa)
(tana)(cosa) - (cosa)(tanb)/cosa + (tana)(cosa)(tanb)
= cosa(tana - tanb)/cosa(1 + tanatanb)
(cosas cancel out)
= (tana - tanb)/(1 + tanatanb) ≡ tan(a-b)
