find the value of p if mean of the following data is 20
x 15 17 19 20+p 23
f 2 3 4 5p 6

we know , mean = ​ 
using this formula we fing the sum of observations and ivide it by the number of observations as follows :
 15x2 + 17x3 + 19x5 + 20+p x 5p + 23x6  2+3+4+6+5p 
= 295 + 100p + 5p2 = 20 ( 15 + 5p ) ( taking the equation to the right hand side as we know mean =20) 
295 +100p +5p2 = 300 + 100p ( cancel 100p from rhs and lhs ) 
295 +5p2 = 300 ( take 295 to rhs) 
​5p2 = 300 - 295 = 5 
p2= 5/5 = 1
p = root of 1= 1