Problem: The sum of the even numbers between 1 and n is 79*80, where n is an odd number, then n=?
The answer to the question is n=79.
but my calculation derives n = 159 based on S=a*(n-1)/2 + 1/2*(n-1)/2*((n-1)/2-1)*d = 79*80, where a=2 and d=2.
Any one can help?
Thanks!
The answer to the question is n=79.
but my calculation derives n = 159 based on S=a*(n-1)/2 + 1/2*(n-1)/2*((n-1)/2-1)*d = 79*80, where a=2 and d=2.
Any one can help?
Thanks!
Yiliang
