Question

The average of five no.s is 51. If average of first 3 no.s is 42 and average of last 3 no.s is 59, then what is the third number??

Answer 1

Let the numbers be a,b,c,d and e
(a+b+c+d+e)/5 =51
⇒(a+b+c+d+e)= 255____(1)
(a+b+c)/3 = 42
⇒(a+b+c) = 126_____(2)
and (c+d+e)/3 =59
⇒(c+d+e) = 177____(3)
adding, (2) and (3) and subtracting with (1),
(a+b+2c+d+e) -(a+b+c+d+e) =303 - 255 = 48
⇒third number, c= 48

Answer 2

Let the no be a,b,c,d,e.
Acc. to question
(a+b+c+d+e)/5=51
a+b+c+d+e=255-------1
Now acc to ques
(a+b+c)/3=42
a+b+c=126
a+b=126-c---------2
(c+d+e)/3=59
d+e=177-c---------3
On putting the value of 2 and 3 in 1 we get,
126-c+c+177-c=255
c=48
therefore third no is 48
d+e=