PPP: CFAI Reading 16 Question 19a

Galli

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Hi All,
Question aks what the expected FX rate should be if the inflation index in country A went from 100 to 150 and in country b went from 100 to 140.
I simply did 140/150 = .9333 x prior Spot rate to arrive at my revised FX-rate of 2.8.
The answer in the book is 2.7 based on a 10% difference in the inflation indecies. (50% country A, 40% country B). and therefore the revised spot rate is 3.00 * .9 = 2.7.
Been awhile since i’ve done the math on PPP but I thought the calc would have been 1+40% / 1 + 1 + 50% which would have arrived at the answer I calculated. Why are they using 10% to calculate the appreciatation of country B’s currency?
 
They’re using the approximation to the inflation differential; you’re using the actual calculation.
The upshot is that you’re correct and they’re not.
 
A little onservation, isn’t %Change Sf/d= % Change Inf Sf/d?
 
S2000magician wrote:
They’re using the approximation to the inflation differential; you’re using the actual calculation.
The upshot is that you’re correct and they’re not.
Thanks S2000 for confirming!
 
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