Help Pls !?

Question

How many terms of the sequence 18, 16, 14 ... should be taken so that their sums is zero ?

Help !!!!!!!!!!!!!!!!!!

Answer 1

18 through -18... so 19 even numbers =)

Answer 2

Think about what it's saying.... you are going to list out numbers in the pattern above, then add those numbers together. When you are done adding, they have to equal zero.

So how can you get a string of numbers to equal zero if you aren't subtracting them? Hint: adding a negative number is the same as subtracting a positive. So for example 3 + (-3) = 0.

If you start listing even numbers in decreasing order, you will eventually get to zero. Keeping going with the negative even numbers and eventually you will see that you can get all of the terms in your sequence to cancel each other out... 2 + (-2) = 0, 4 + (-4) = 0, etc. Once you get that far, simply count up how many numbers you wrote down.

Make sense? With these types of problems you have to think outside the box. When people think numbers, they only think greater than zero, the "counting numbers". There's nothing in the question that says you can't use numbers less than zero. They also forget that the number line continues left of zero (and that there are fractions and decimals between the integers!). Good luck!

Answer 3

this is a question of arithmatic progreesion(A.P.)
here first term(a)=18, common difference(d)= -2
let n terms are added so that sum is equal to zero.
Sn =n/2[2a+(n-1)d]
0=n/2[2*18 + (n-1)*(-2)]
0= n/2[36-2n+2]
0=38-2n
2n=38
n=38/2
n=19
so 19 terms must be added to get zero as sum.