X $4000
Y $6000
Explanation:
Let w be invested in Stock X,
Correlation = -1
Standard Deviation = w(0.75) - (10,000 - w)(0.50)
So,
For standard Deviation to be 0,
0 = 0.75w - 5,000 + 0.50w
w = $4,000
Amount invested in Stock X = $4,000
Amount invested in Stock Y = $6,000