Hi :)

I'm having some difficulty with the following problem. Evaluate

The book I'm reading doesn't have an example where the two numbers above the sigmas are different, but does have an example where they are the same. So I'm not sure how to approach this one. I had a bash but came up with the incorrect answer (book says it should be 210)

As I looked at it further I became even more confused, since

*i* ranges from 1 to 5, then when

*i*=5 the inner sum ranges from 5 to 4? I don't see how that makes sense

If anyone could shed any light on this or point me in the right direction to solve it, it would be much appreciated.