a fill - 1/20 per minute
b fill - 1/30 per minute
c can empty - 1/40 per minute


Suppose this take x minute

1 x +1x - 1x
---  --  ----  =1
20   30   40

Solve this x=17(approximately)

120/7

99/1020

-0.2

1/10 is = 0.1
so (1/10)18=1.8
lly (1/10)20=2.0
so 1.8-2.0=-0.2

answer is = -0.2

(1/10)^18 - (1/10)^20
= 1/(10^18) - 1/(10^20)
= (10^2 - 1)/(10^20)
= 99/(10^20)

Yes we can. All the information will be stored in encrypted
form in memory. During fetching, it must be first decrypted
by operating system and then can be read.

Ensuring that various cryptographic keys are provided by 
their intended users, and only for their intended purposes, 
temper resistent hardware is introduced.

An example temper resistent device is your "SMART CARD".

You have to physically posess the device and also have to 
possess the PIN or the password to use it.

those are technics like
face detection
Iris recognition
fingerprint recognition
palm vien recognition.
All these can be used for Authentication

The science of cryptography has existed in one form or 
another for centuries.
Cryptography is the art of encoding and decoding messages 
for transmission between two
parties, while keeping the message secret from unwanted 
viewers. There are many common
implementations of cryptography in use today such as the 
HTTPS protocol on the Internet. All
forms of data encryption and cryptography require a key in 
some form or another for use in
encoding and decoding data. There are even some modern 
methods of encryption that have been
mathematically proven to be unbreakable if they are 
implemented properly.
The inherent problem with any form of cryptography is in 
the method of key distribution.
To date, all forms of message encryption have possessed 
this major vulnerability. As such, it
makes no difference whether a secret message is sent via 
homing pigeon, a radio transmission, a
penciled message on a notepad, or whispering to another, 
there is no physical way to get a
cryptographic key to another without running the risk of 
the key being intercepted.
To solve this dilemma, a radical solution has been proposed 
called quantum
cryptography. This method essentially uses photon light 
particles to send a key to an intended
recipient. The difference with this method of key 
distribution is that it implements quantum
mechanic’s uncertainty principle as a means to guarantee 
the privacy of a key during
distribution. Practically, quantum cryptography has the 
ability to afford complete privacy during
the entire broadcast of an encoded message.

In quantum computing, we use the concept of qubits, 
superposition and coherence. A normal bit can be in only 
two states - 0 and 1. But a qubit it can be in 0, 1, or in 
the superposition of 0 and 1.


Quantum computers, will be much much faster than 
traditional silicon based compuers.