Divide a number 100 into two parts such that their product is maximum.
50,50
25,75
60,40
90,10
Let the two parts be x and (100-x)
Product,
P=x(100-x)=100x-x2
For P to be maximum or minimum,
dPdx=100-2x=0
x=50
d2Pdx2=-2
i.e. P is maximum at x =50
Dividing equally the two parts are (50,50)