Question

If 1 + 2+ 3+ ...... + n = 666 find n:

• A. 30
• B. 36
• C. 33
• D. 39

Answer 1

Answer:

B. 36

$1 + 2+ 3+ ...... + n = 666$

$n(n+1)/2=666$

$n(n+1)=1332$

$n^2+n=1332$

$n^+n-1332=0$

$(n+37)(n-36)=0$

$n=36$