Posted by SHANA on Tuesday, September 11, 2012 at 10:07pm.
You have to break 1260 down into it's number tree. Start by dividing the number by 2 until you can't do it evenly, then divide by 3, and so on until no more divisions can be made:
1260/2 = 630
So we have one prime factor, 2 and are left with 630:
630/2 = 315
Now we have two prime factors, 2 and 2. We are left with 315:
315/3 = 105
Now we have three prime factors - 2,2,3. We are left with 105:
105/3 = 35
Now we have four prime factors - 2,2,3,3. We are left with 35:
35/5 = 7
Now we have SIX prime factors - 2,2,3,3,5,7. Thus the sum of all the distinct, positive prime factors of 1260 are:
2+2+3+3+5+7 = 22