need help regarding Q Function

[moonnightingale]

Can any body explain me how the book solved this Q FUNCTION PROBLEM

 

[saeddawoud]

Can any body explain me how the book solved this Q FUNCTION PROBLEM

Try to understand it as following:

If Q(x)=a, then x=? i.e: what value of x that gives Q(x)=a? Try to look up using Q-function table.

See the graph here.

 

[moonnightingale]

Thanks a lot for posting this graph and making my concept clear.
Yes u r right in saying that i assume it Q(x)= 0.9 i understand all this but in exam, i will not be having graph and we are given Q table.
I also know how he has written -1.28 from table. I have devised a crude method for values greater than 0.5.

To solve for 0.9. subtract 0.9 from 1
1- 0.9 = 0.1
Now look for Q inverse in table, as u can see that if x is 1.28, then Q(x) is 0.1003
so answer is 1.28 and put (negative sign with it)

But what is technical reason for all this, why negative sign ,,,, why 0.1 i want to understand its concept. Hope u got me

The table is also attached

 

[saeddawoud]

You are on the right tract. Note that 1-Q(x)=Q(-x).

Regards