Let 's say we are looking for the sum of three digit

Question

Let 's say we are looking for the sum of three digit integers that are divisible by 9. 

so sum = average * number

For the number:

take the high number 999/9 = 111
and the low number in the range 108/9=12

so we have 111-12 +1= 100 

For the average do we use (1000+100)/2, (999+108)/2, or do we use (111+12)/2?

Dek · Answer

Since we need to find the avg of numbers from 108 to 999, and they are consec, avg should be 999+108/2

skinsvt · Answer

Anyone else to break the tie?

vidyasagar · Answer

A.P. = a.....b...c...............................L (last)
 = 108......................................999

sum = (a+L)*n/2...............n=total no. of Numbers in the series=100 here
 = (a+L)/2 * n
 = Avg.  *n
 =  (108+999)/2  *100

grad_mba · Answer

q) to find the sum of all 3 digit numbers divisible by 9

Followed this approach-

1st number : 9x12 = 108 / last number = 9x111 = 999

hence total # of 3 digit numbers = (111-12)+1 = 100

a1 = 108
an = 999
n = 100

so sum = n/2(a1+an) !

Let 's say we are looking for the sum of three digit

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