Answer:
Investing today is a better option because it has a better NPV of $2.3398 million 
Explanation:
Given data : 
<u>For Today's Investment </u>
Initial capital investment = $4 million
positive cash flow = $2 million
period of cash flow = 4 years
project cost of capital = 10%
To get the value of This option we have to determine the NPV of this option
NPV = PMT * ![[\frac{1-(1+r)^-4}{r} ] - initial cash flow](https://tex.z-dn.net/?f=%5B%5Cfrac%7B1-%281%2Br%29%5E-4%7D%7Br%7D%20%5D%20-%20initial%20cash%20flow) ----------- (1)
   ----------- (1)
PMT = $2 million
r = 10%
initial cash flow = $4 million
Equation 1 becomes 
NPV = (2 * 3.1699 ) - 4
         = $6.3398 - $4 =  $2.3398 million 
<u>For later investment ( 2 years )</u>
initial capital investment = $5 million
90% chance of positive cash flow = $2.1 million
10% chance of positive cash flow = $1.1 million
project cost of capital = 10% 
NPV value for a cash flow of $1.1 million
NPV = PMT * ![[\frac{1-(1+r)^-4}{r} ] - initial cash flow](https://tex.z-dn.net/?f=%5B%5Cfrac%7B1-%281%2Br%29%5E-4%7D%7Br%7D%20%5D%20-%20initial%20cash%20flow)
PMT = $1.1 million
initial cash flow = $5 million
r = 10% 
Hence NPV = ($1.1 * 3.1699 ) - $5 million
                     = $3.48689 - $5 million
                     = - $1.51311  
therefore the present NPV =   - $1.51311 / 1.21 =  -$1.25 million  ( therefore no investment will be made ) 
NPV value for a cash flow of $2.1 million
NPV = PMT * ![[\frac{1-(1+r)^-4}{r} ] - initial cash flow](https://tex.z-dn.net/?f=%5B%5Cfrac%7B1-%281%2Br%29%5E-4%7D%7Br%7D%20%5D%20-%20initial%20cash%20flow)
PMT = $2.1 million
initial cash flow = $5 million
r = 10% 
hence NPV = ($2.1 * 3.1699 ) - $5 million
                    = $6.65679 - $5 
                    = $1.65679
therefore the present NPV = $ 1.65679 / 1.21 = $1.369 million 
The Expected NPV value of later investment ( after 2 years ) 
= $0 * 10% + $1.369 * 90% 
= $1.2321 million