Question

Average of four number is 30. If sum of three number is 85, then find the fourth number.

Answer 1

Answer:

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. 

Answer 2

Answer:

35

Step-by-step explanation:

Let the numbers be a, b, c, d.

As given,

( a + b + c + d ) / 4 = 30

a + b + c + d = 120 ----- ( 1 )

Also,

a + b + c = 85 ----- ( 2 )

By ( 1 ) - ( 2 ),

( a + b + c + d ) - ( a + b + c ) = 120 - 85

d = 35

Thus, ANS = 35