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# Black-Scholes N(-d1) & N(-d2)

#### SamuelMartin

##### New Member
ok, I always seen in all the exercises that when calculation the price of a Put to convert the d1 into -d1 you need to do --> -d1 = 1 - d1

However, I don't know in the following exercise solution, where the -d1 & -d2 figures are coming from.

Any help would be highly appreciated.

Thanks!!!!!

QUESTION IS IN THE PICTURE ATTACHED.

#### ShaktiRathore

##### Well-Known Member
Subscriber
Hi,
We do the conversion -d1=1-d1 only for N(d1) so that if we know N(d1) then we can find N(-d1)=1-N(d1).for normal dist. U know that for any vatiable x N(-x)=1-N(x) as its symmetrical.doont confuse as -d1 and- d2 shall have same magnitude as d1 and d2 only their signs shall change there is no identity as -d1=1-d1 its useful in conjunction of N(d).
Thanks

#### SamuelMartin

##### New Member
So the explanation of the exercise and the result is wrong?

That's what I thought N(-d1)=1-N(d1) and how I always calculated but the answer of the exercise confused me.

Thanks

#### David Harper CFA FRM

##### David Harper CFA FRM
Staff member
Subscriber
Hi @SamuelMartin The explanation looks correct to me. I don't see it showing N(d1) or N(d2). It computes d1 = 0.2417 and d2 = 0.0917, then it just negates the d1 and d2: N(-d2) = N(-0.0917) = 0.4634 and N(-d1) = N(-0.2417) = 0.4045.

I wonder if you are focused (as I am) on N(-d1) = 1 - N(d1) because you'd need most likely to use this on the exam, but the answer does not show it that way. What I mean is, the Z lookup table is typically provided only for the positive Z values (the right side of the distribution). So, in this problem, you'd need d1 = 0.2417 to retrieve N(d1) = 0.595, which is based on a rounded N(0.24). Then you'd get N(-d1) = 1 - N(d1) = 1-0.595 = 0.405 ... because with a hardcopy lookup table you probably wouldn't be able to retrieve N(-0.2417) directly. I hope that's helpful, thanks,

#### JFZ2014

##### New Member
Hi, a side question: where is the BS model spreadsheet? I would like to study it and saw a video on it saying that it is here.
Many thanks!

#### JFZ2014

##### New Member
Thanks Nicole. I clicked on the link and was directed to:
Could you check if I have purchased or subscribed? Thanks. I thought I did. If not, please let me know. Thanks.

#### SamuelMartin

##### New Member
Hi @SamuelMartin The explanation looks correct to me. I don't see it showing N(d1) or N(d2). It computes d1 = 0.2417 and d2 = 0.0917, then it just negates the d1 and d2: N(-d2) = N(-0.0917) = 0.4634 and N(-d1) = N(-0.2417) = 0.4045.

I wonder if you are focused (as I am) on N(-d1) = 1 - N(d1) because you'd need most likely to use this on the exam, but the answer does not show it that way. What I mean is, the Z lookup table is typically provided only for the positive Z values (the right side of the distribution). So, in this problem, you'd need d1 = 0.2417 to retrieve N(d1) = 0.595, which is based on a rounded N(0.24). Then you'd get N(-d1) = 1 - N(d1) = 1-0.595 = 0.405 ... because with a hardcopy lookup table you probably wouldn't be able to retrieve N(-0.2417) directly. I hope that's helpful, thanks,

David,, you are awesome. You provide me with the answer I was looking for. I understand now. I was doing 1 - 0.09 = 0.93 so I was obviously wrong.

Thanks again

#### Nicole Seaman

##### Director of FRM Operations
Staff member
Subscriber
Hello
Thanks Nicole. I clicked on the link and was directed to:
Could you check if I have purchased or subscribed? Thanks. I thought I did. If not, please let me know. Thanks.
@JFZ2014,

I checked your account, and you purchased the Basic package. In order to access the spreadsheets, you need to be subscribed to the Professional package. If you are interested in upgrading, we do offer upgrades for the difference in price between the packages.

Thank you,

Nicole

##### New Member
hi Nicole,
i cannot see any spread sheets related to Black scholes model and binomial model in study planner. As I am using the professional package can you please help me out.