二、(20%) Bowl B₁ contains 2 white chips, bowl B₂ contains 2 red chips, B₃ contains 2 white and 2 red chips, and B₄ contains 3 white chips and 1 red chip. The probability of selecting bowl B₁, B₂, B₃, B₄ are 1/2, 1/4, 1/8, and 1/8, respectively. A bowl is selected using these probabilities, and a chip is then drawn at random. Find (a) P(W), the probability of drawing a white chip.

五、(25%) To test two method of instruction, 50 students are selected at random for each of two groups. At the end of the instruction period each student is assigned a grade (A, B, C, D, or F) by an evaluating team. The data are recorded as follows: | | Grade | | | | | | | --- | --- | --- | --- | --- | --- | --- | | | A | B | C | D | F | Total | | Group I | 8 | 13 | 16 | 10 | 3 | 50 | | Group II | 4 | 9 | 14 | 16 | 7 | 50 | Please use a chi-square test with α = 0.05 to test the equality of the distributions of grade. The critical value of chi-square distribution for above test is as follows: | r | 2 | 3 | 4 | 5 | 6 | | --- | --- | --- | --- | --- | --- | | χ²₀.₀₅(r) | 5.991 | 7.815 | 9.488 | 11.070 | 12.590 | | χ²₀.₀₂₅(r) | 7.378 | 9.348 | 11.140 | 12.830 | 14.450 | | * P(≥χ²ₐ(r)) = α for X ~ χ²(r). | | | | | |

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