Find the value of p, if the mean of the following distribution is 20.
x: | 15 | 17 | 19 | 20+p | 23 |
f : | 2 | 3 | 4 | 5p | 6 |
X | f | fx |
15 | 2 | 30 |
17 | 3 | 51 |
19 | 4 | 76 |
20 + p | 5p | 100p + 5p2 |
23 | 6 | 138 |
∑f = 15 + 5p | ∑fx = 295 + 100p + 5p2 |
Mean, 
= 
20 = 
60 + 20p = 59 + 20p + p2
p2 – 1 = 0
p = 1
8