UDD

Hi,

I wanted to check if linear interpolation can be used for udd in all cases
for e.g.
September 2017 Q3
(L87.5)/(L85.5)
where L87.5 = L87 +0.5(L87 - L88)

If not, why is it the case?

Thanks,
Aaron

 

Hi mate,
The interpolation formula you stated is slightly wrong.
The correct formula here would be:
L87.5= L87 + 0.5(L88-L87)

L88-L87 has to be negative since L87>L87.5>L88.
So your answer will eventually turn out in between L87 and L88.
Algebraic proof of the formula is:


Hope this helps you !

 

Thanks for this,

But it seems I have made a mistake,
Rephrased:

We are looking for L87.75
x=87.75 y=L87.75
x1=87 y1=L87
x2=88 y2=L88

(87.75-87)/(88-87) = (L87.75-L87)/(L88-L87)

=> L87.75 = L87+0.75(L88-L87)

calculating gives:
L87.5 = 14280+075(11874-14280)
=12475.5

... which actually is the same as the solution
My bad - i thought this lead to a difference - thanks