Mathematical probability question.?

Question

40% of ppl clean their car windows property after a snow storm. If you randomly observe 20 cars, what is the probability that fewer than 12 but more than 6 have had their windows properly cleaned?

Answer 1

Binomial distribution:

Probability
= ∑C(20,i)(0.4^i)(0.6)^(20-i), i from 7 to 11
= binomcdf(20,.4,11) - binomcdf(20,.4,6)
= 0.693462961

Answer 2

69.346+ % for 7 through 11 inclusive (less than 12, greater than 6).


Yahoo Answers will remove the formatting from this, but here goes anyway:

n C(20,n) 0.4^n 0.6^(20 - n) Prob(exactly n)
== ====== ============= ============= ================================

0 1 1.000000e+000 3.656158e-005 0.000036561584400629740000000000
1 20 4.000000e-001 6.093597e-005 0.000487487792008396520000000000
2 190 1.600000e-001 1.015600e-004 0.003087422682719845300000000000
3 1140 6.400000e-002 1.692666e-004 0.012349690730879383000000000000
4 4845 2.560000e-002 2.821110e-004 0.034990790404158249000000000000
5 15504 1.024000e-002 4.701850e-004 0.074647019528870956000000000000
6 38760 4.096000e-003 7.836416e-004 0.124411699214784930000000000000
7 77520 1.638400e-003 1.306069e-003 0.165882265619713250000000000000
8 125970 6.553600e-004 2.176782e-003 0.179705787754689400000000000000
9 167960 2.621440e-004 3.627971e-003 0.159738478004168350000000000000
10 184756 1.048576e-004 6.046618e-003 0.117141550536390120000000000000
11 167960 4.194304e-005 1.007770e-002 0.070994879112963719000000000000
12 125970 1.677722e-005 1.679616e-002 0.035497439556481852000000000000
13 77520 6.710886e-006 2.799360e-002 0.014563052125736149000000000000
14 38760 2.684355e-006 4.665600e-002 0.004854350708578716900000000000
15 15504 1.073742e-006 7.776000e-002 0.001294493522287658100000000000
16 4845 4.294967e-007 1.296000e-001 0.000269686150476595480000000000
17 1140 1.717987e-007 2.160000e-001 0.000042303709878681640000000000
18 190 6.871948e-008 3.600000e-001 0.000004700412208742405100000000
19 20 2.748779e-008 6.000000e-001 0.000000329853488332800310000000
20 1 1.099512e-008 1.000000e+000 0.000000010995116277760013000000

Answer 3

huh, you cant calculate that , you also have to give the probability density function. 40% is not enough information.