Total cost: C(Q)=∫C'(Q)dQ.

=∫2dQ

=2Q+C0

∫C(0)= 0

∴C 1=0

C(Q)=2Q

Total income: R(Q)=∫R'(Q)dQ.

=∫(7-2Q)dQ

=7Q-Q^2+C 1

∫R(0)= 0

∴C 1=0

R(Q)=7Q-Q^2

Let the total profit be L(Q)

L(Q)=R(Q)-C(Q)

=7Q-Q^2-2Q

=-Q^2+5Q

=-(Q-5/2)^2+(5/2)^2

=-(Q-2.5)^2+6.25

When the output Q=2.5 hundred units =250 units, the maximum profit is 62,500 yuan.

(2) Q=250+50=300 sets =300 sets.

L(Q)=-(3-2.5)^2+6.25

=-0.25+6.25

= 60,000 yuan

Total profit decreased: 6.25-6=0.25 million yuan.