Question

Which is the sum of the sequence {5*1, 5*8, 5*27, 5*64, 5*125, 5*216}?

Answer 1

2160

Explanation:

I find that it is easier to split the sequence into smaller, more manageable sections. For numbers beyond 13, the simplest way is to split it up into place values.

Note: * is a multiplication symbol

5*1 = 5

5*8 = 40

5*27 = (5*20) + (5*7) = 100+35 = 135

5*64 = (5*60) + (5*4) = 300+20 = 320

5*125 = (5*100) + (5*20) + (5*5) = 500+100+25 = 625

5*216 = (5*200) + (5*10) + (5*6) = 1000+50+30=1080

Now you can add all of the totals up!

135+320+625+1080 = 2160