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In a set of X consecutive numbers, the first number is 4. [#permalink]

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19 Feb 2004, 09:05

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

In a set of X consecutive numbers, the first number is 4. Which of the following expressions is the average of the set?
a. 4 + x/2
b. (4+x)/2
c. (7+x)/2
d. 4*x/2
e. (3+x)/2

No I didnt plug it in. I first tried with some numbers and then with another one and then went for the choices. This problem can be done within 1 min or may be less than that.

I could not come up with formula. Tried to derive it for about 5 mins then plugged in some values and got the answer. Let us knowwhat is the correct one

Sum of 1st x consecutive integers is= x(x+1)/2
Since 1st integer is 4, therefore sum of x-3 integers is = x(x+1)/2- (1+2+3)
= x(x+1)/2 - 6
Average = {x(x+1)/2 -6}/x-3 = (x+4)/2

Sum of 1st x consecutive integers is= x(x+1)/2 Since 1st integer is 4, therefore sum of x-3 integers is = x(x+1)/2- (1+2+3) = x(x+1)/2 - 6 Average = {x(x+1)/2 -6}/x-3 = (x+4)/2

Sum of 1st x consecutive integers is= x(x+1)/2 Since 1st integer is 4, therefore sum of x-3 integers is = x(x+1)/2- (1+2+3) = x(x+1)/2 - 6 Average = {x(x+1)/2 -6}/x-3 = (x+4)/2