Question

Average of 3 numbers is 17 and that of the first two is 16 find third

Answer 1

Let the 3 numbers be a,b and c.
Given: average of 3 numbers= [(a+b+c)/3]=17
=> a+b+c= 51 {multiplying both the sides of above equation by 3}—————eq 1
Also, it is given that the average of 2 numbers= [(a+b)/2]=16
=> a+b=32 {multiplying both the sides of above equation by 2}—————eq 2
Substituting eq 2 in equation 1,
32+c=51
c=51–32
c=19
Hence the third number is 19.

Answer 2

$\Large{\textbf{\underline{\underline{According\;to\;the\;Question}}}}$

Given,

Average of 3 numbers = 17

Average of first 2 numbers = 16

Assume,

Three numbers be p , n and t

Information,

$\rm \: \: \: \: \: \: \: \: \:\dfrac{p+n+t}{2}=17$

p + n + t = 34 .....(1)

Now,

$\rm \: \: \: \: \: \: \: \: \:\dfrac{p+n}{2}=16$

p + n = 32 .....(2)

Putting this value in (1) we get :-

p + n + t = 34

32 + t = 34

t = 34 - 32

t = 2

Therefore,

Third number = 2