Hi. Can anyone explain to me how you determine the 25 delta to 10 delta r/r and strangle ratios?ThanksAsif

Your questions is rather unclear... What do you mean "how"? Forgive me for being droll, but I believe it's done through a process called "arithmetic" .

Sorry I mean I wasn't clear, My senior trader told me that the R/R ratios from 25d to 10d should be about 1.8, but he could not explain how that 1.8 was reached, and I suspect he doesn't know.Can someone explain this to me, and what you mean by arithmetic process?

You just take one number and divide it by the other number. That's what I am referring to as "arithmetic".I am probably still not understanding your question correctly.

Disclaimer : FX is not my primary market, so hopefully someone who knows more than me can confirm or deny the following in a more rigorous fashionThe rr and bf quotes are linear wrt to the vols, so parallel shifts in the IV curve wont affect these ratios. Hence, the ratio of the rr10 to rr25 gives an indicator of skewness in the market that is independent of volatility levels, and the strangle likewise for the convexity of the curve. By saying that this ratio is about 1.8 I would understand this to mean that there is a level of skewness in the vol curve that is considered normal, and this corresponds to an rr ratio of around 1.8. Should the ratio move significantly away from this number it would represent a deviation from typical historical vol curve shapeMy understanding is that this number is simply a historical ratio specific to each currency, and not based on anything theoretical

Yes you are correct. This kind of "extrapolation" is sometimes done in very illiquid crosses.