Need help with a math addition formula

• Parka

  9 Jan 09, 21:34

  If every month increases by 50, what's the total at the end of the year? E.g. 50 100 150 200 250 The cumulative sum will be 50 150 300 500 750 Pain in the brain already.
• tut4nkh4m3n

  9 Jan 09, 21:51

  add every month man, there's only twelve...

• Eyelessz

  10 Jan 09, 00:59

  Let n be 50?

  n + 2n + 3n + 4n + 5n + 6n + 7n + 8n + 9n + 10n + 11n + 12n = 78n

  78 x 50 = 3900

  I could be wrong ...

• eagle

  10 Jan 09, 08:54

  Sounds like E maths to me... Number patterns...

  This is an Arithmetic Progression

  Term n = 50 + (n-1)(50)    (a + (n-1)d, where a is first term, d is common difference)

  So, the sum of n terms is (n/2)(2a + (n-1)d)
  Sum here is (12/2)(100 + 50n - 50) = (50 + 50n)*12

  So end of the year, you get 6 * (50 + 50*12) = 3900

   

  Alternatively, you could also find sum of n terms by (n/2)(first term + last term)
  first term = 50
  last term = 50 * 12 = 600
  So, sum = 6* 650 = 3900

   

  Lastly, you could also do what the forumers said above, which is to add up each individual month.