Formula to return percent of change in last 2 cells at end of row

[thorsmath]

If I have a list of data from b3 to b8, for example, what formula will subtract b8 from b7 and then calculate the percentage of change and display the
result in b2? (b1 will have a text title) Now here's the tricky part... I will constantly be adding new data and inserting it at the end of the row and the formula must adapt to always perform the calculation on the last 2 cells in the row.

I understand the basic concept of ((b8-b7)/b8)*100 to get the percentage. What I can't do is figure out how to use functions to make sure that this operation is always performed on the last 2 cells in the row no matter how many times I add data.

Example.. When I add a value to b9, the formula must now return results for b8 and b9. When I add to b10, it must work on b9 and b10, etc....

[martindwilson]

=(INDEX($B$3:$B$203,MATCH(9.9999E+37,$B$3:$B$203,1))-INDEX($B$3:$B$203,MATCH(9.9999E+37,$B$3:$B$203,1)-1))/INDEX($B$3:$B$203,MATCH(9.9999E+37,$B$3:$B$203,1))*100
with 100 in b8 and 50 in b7
will give 50
but leave of the *100
gives 0.5 format cell as % will give 50%

[thorsmath]

Ooops! Thank-you for the response; however, I mis-communicated my situation. I gave example numbers for columns, when I should have been using row designations. In other words, I should have said the text title will be in A2, the result would go in B2, and the data would be in C2-J2. I would be adding data at the end of the row in K2, L2, M2, etc.

Does that make sense?

[martindwilson]

no problem just change to row
try

=(INDEX($C$2:$IV$2,1,MATCH(9.9999E+37,$C$2:$IV$2,1))-INDEX($C$2:$IV$2,1,MATCH(9.9999E+37,$C$2:$IV$2,1)-1))/INDEX($C$2:$IV$2,1,MATCH(9.9999E+37,$C$2:$IV$2,1))

[thorsmath]

This formula works very well. Thank-you for your assistance. Greatly appreciated.