Question

Can't understand this. Can anyone tell me the answer -

Answer 1

Hi,

The first thing you have to remember, that the sum of  all probabilities are equal to 1.

As you have only  4 items  :   Pasta + Fish + Pizza +Salad

So pasta + fish + pizza +salad  =   1  

1 means every client who bought something had something to eat.  

So now it simple :

We know  the probability of every other items, so we will find the probabilty of  salad by substracting  off  1 every other probabilities.  

Remind yourself  to always have data in same shape/ units etc.

Here we have percentage, fraction, numbers.... can be confusing.  

So convert all in same shape.  I 'm going to convert all in numbers, as it seems to me the simpliest.

I will call probability of  salad  "X" as it usually like that we call something unknown in math.

So pasta =  15 % =  15/100  = 0.15

    fish =  0.2

    pizza =  3/10 = 0.3

   salad =  X

So  now  we have  :  

pasta + fish + pizza +salad  =   1  

replace by what I know :

0.15 +0.2+0.3 + X = 1

0.65 + X = 1  

0.65 +X -0.65 = 1 - 0.65

                         X =  0.35

Salad probability is  0.35  , which means  35 % .