4 M9 u; W' X7 N5 X5 n0 C% q! m. f0 [# \1 ^# L y1 u
No.11 5 `, V X- [; P1 U
(1) When events A and B are independent, P(A and B) = P(A)P(B)0 M# C( x+ B0 V$ |9 F
(2) 1 K' P* r* T n0 }/ P( X
7a + 77b = 350 -----> a + 11b = 50; T; B" I( s9 |1 Q% w$ z9 L
n = a + b = 50 - 11b + b = 50 -10b7 }1 P8 E, h, _4 l
so n = 50 or 40 or 30 or 20 or 10