to sum columns

[js]

A B C D E
1 1 2 3 4 5
2 361 311 296 247 303
3 596 562 234 979 536
4
5

Say cell B5 contents 4. What is the formula to sum columns with no of
columns based on cell B5 (column A2 to D2)?

Thanks

js

 

[Max]

One way
In C5: =SUM(OFFSET(A2,,,,B5))
where B5 contains: 4