If the value in Column A are always indexing by 10 then will this formula
return the proportional response that you are looking for?

=IF(FLOOR(C1,10)=C1,VLOOKUP(C1,A2:B6,2,TRUE),VLOOK UP(C1,A2:B6,2,TRUE)-(C1-FLOOR(C1,10))/(CEILING(C1,10)-FLOOR(C1,10))*((INDEX(B2:B6,MATCH(FLOOR(C1,10),A2: A6,FALSE)))-(INDEX(B2:B6,MATCH(CEILING(C1,10),A2:A6,FALSE)))))

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"jatman" wrote in message
...
i have the following data:
A B
1 10 140
2 20 95
3 30 70
4 40 60
5 50 55

in C1 i enter 20, in D1 i have the formulae as follows:
= vlookup(C1,A:B,2,FALSE) and the return result is 95. can the formula be
changed so that it can look up a number (average) that is not in the A
column. example vlookup 35 returns a value of 65, or 31 returns a value
of
69?

thank you,

jat