about probability problem!!!!

Given:
Peter and John each shoots twice.
Probability that Peter hits a target in a shot i.e. Pp (Peter hits a target in a shot)= 1/5.
Probability that John hits a target in a shot i.e. Pj(John hits a target in a shot ) = 1/4.
Solutions:
(a) Probability that the target is not hit
= P(Peter does not hit target in both shots)*P(John does not hit target in both shots)
= [P(Peter does not hit target in shot i)*P(Peter does not hit target in shot ii)] * [p(John does not hit target in shot i)*P(John does not hit target in shot ii)]
= [(1-Ppi)*(1-Ppii)] * [(1-Pji)*(1-Pjii)]
= [(1-1/5)(1-1/5) * (1-1/4)(1-1/4)]
= (4/5)(4/5)(3/4)(3/4)
= 9/25 or 36%


(b) Probability that the target is hit
= 1 - Probability that the target is not hit
= 1 - 9/25
= 16/25 or 64%

(c)(1) Probability that only one person hits
= [P(Peter hits in shot i and/or shot ii) * P(John does not hit in both shots)] + [P(Peter does not hit in both shots) * P(John hits in shot i and/or shot ii)]
= (Ppi)(1)*(1-Pji)(1-Pjii) + (1-Ppi)(1-Ppii)*(Pji)(1)
= (1/5)(1)*(1-1/4)(1-1/4) + (1-1/5)(1-1/5)*(1/4)(1)
= ( 1/5)*(3/4)(3/4) + (4/5)(4/5)*(1/4)
= 9/80 + 4/25
= (45+64)/400
= 109/400 or 25.23%
(c)(2)Probability that only one shot hits
= P(Peter only hits one and John does not hit twice) + P(John only hits one and Peter does not hit twice)
= [P(Peter hits in shot i and not shot ii) + P(Peter hits in shot ii and not shot i)] *P( John does not hit twice) + [(P(John hits in shot i and not shot ii) + P(John hits in shot ii and not shot i)]* P(Peter does not hit twice)
= [(Ppi)(1-Ppii) + (Ppii)(1-Ppi)]*(1-Pji)(1-Pjii) + [(Pji)(1-Pjii) + (Pjii)(1-Pji)]*(1-Ppi)(1-Ppii)
= [(1/5(1-1/5)+(1/5)(1-1/5)]*(1-1/4)(1-1/4) + [(1/4)(1-1/4)+(1/4)(1-1/4)]*(1-1/5)(1-1/5)
= (8/25)(3/4)(3/4) + (3/8)(4/5)(4/5)
= 9/50 + 12/50
= 21/50 or 42%

a)P(the target is not hit ) = P(peter not hit twice and john not hit twice)
= 4/5 * 4/5 * 3/4 * 3/4
= 9/25
b)P(the target is hit) = 1- P(the target is not hit ) = 1 - 9/25
=16/25
c)P(only one hit) = P(peter only hit one and john not hit twice) + P(peter not hit twice and john only hit one)

=2 *( 1/5 * 4/5 * 3/4 * 3/4 )+ 2 *( 4/5 * 4/5 * 1/4 * 3/4)
=9/50 + 6/25
=21/50