Question

the average of four number is 50 of first three numbers is 160, the fourth number is​

Answer 1

Average of four numbers = 30

Sum of the first three numbers = 85

Let the fourth number be .  

Now, all the four numbers include the three numbers (whose sum is 85) and the fourth number .  

So, sum of four numbers =  

Now, we know that sum of all observations divided by the number of observations is the average of the given data.  

Now,  

Sum of all four numbers

--------------------------------    =    Average

              4

⇒  

Multiplying both sides of the equation by 4.  

⇒  

Subtracting 85 from both sides.  

⇒  

∴ The fourth number is 35.

Hope this may help you.  

If you have any doubt, then you can ask me in the comments.