Răspuns:
MN = 2*NP
AB = 10 cm
A mijl lui MN => AM = AN => AN = MN/2; MN = 2*AN
B mijl lui NP => NB = BP => BN = NP/2; NP = 2*BN
M, A, N, B, P coliniare => AB = AN + BN
M, N, P coliniare =>
MP = MN + NP = 2*AN + 2*BN = 2*(AN + BN) = 2*AB = 20 cm
MP = MN + NP = 2*NP + NP = 3*NP => NP = MP/3 = 6,(6) cm
=> MN = 2* NP = 13,(3) cm