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(25)×(26)=10×15=150
[2 marks: 1 for correct combinations, 1 for final answer]
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Total arrangements = 5!=120. Arrangements where 2 specific books are together = 2!×4!=48.
120−48=72.
[2 marks: 1 for total/together, 1 for subtraction]
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P(A∪B)=P(A)+P(B)−P(A∩B)⟹0.8=0.6+0.4−P(A∩B)⟹P(A∩B)=0.2.
[2 marks: 1 for formula, 1 for answer]
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P(X∪Y)=P(X)+P(Y)−P(X)P(Y)=0.3+0.5−(0.3×0.5)=0.8−0.15=0.65.
[2 marks: 1 for independent property, 1 for answer]
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P(Red, Red)+P(Blue, Blue)=(107×96)+(103×92)=9042+906=9048=158≈0.533.
[3 marks: 1 for each path, 1 for sum]
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P(A∩B)=P(A)×P(B∣A)=0.7×0.4=0.28.
[2 marks: 1 for formula, 1 for answer]
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Let E be Economics, P be Psychology. n(E∪P)=100−20=80.
n(E∩P)=n(E)+n(P)−n(E∪P)=60+50−80=30.
P(Both)=10030=0.3.
[3 marks: 1 for union, 1 for intersection, 1 for probability]
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X∼B(15,0.5). P(X=8)=(815)(0.5)8(0.5)7=6435×(0.5)15≈0.196.
[2 marks: 1 for formula, 1 for answer]
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X∼B(12,0.25). P(X≥2)=1−[P(X=0)+P(X=1)].
P(X=0)=(0.75)12≈0.0317; P(X=1)=12(0.25)(0.75)11≈0.1267.
1−(0.0317+0.1267)=0.8416.
[3 marks: 1 for complement, 1 for individual probs, 1 for final]
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Mean μ=np=20×0.35=7.
Variance σ2=np(1−p)=20×0.35×0.65=4.55.
[2 marks: 1 for mean, 1 for variance]
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Z=12165−150=1.25. P(Z>1.25)=1−0.8944=0.1056.
[3 marks: 1 for z-score, 1 for table look-up, 1 for final]
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Z1=σ10−μ=−1.0 (since P(Z<−1)≈0.1587); Z2=σ20−μ=2.0 (since P(Z>2)≈0.0228).
10−μ=−σ and 20−μ=2σ.
Subtracting: 10=3σ⟹σ=3.33. μ=10+3.33=13.33.
[4 marks: 1 for each z-score, 1 for system of eq, 1 for values]
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E(3X−2)=3(50)−2=148.
Var(3X−2)=32×Var(X)=9×16=144.
[3 marks: 1 for mean, 2 for variance property]
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P(Z>580−μ)=0.10⟹580−μ=1.282.
80−μ=6.41⟹μ=73.59.
[3 marks: 1 for z-value, 1 for equation, 1 for μ]
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xˉ=812+15+11+18+14+16+13+17=8116=14.5.
[2 marks: 1 for sum, 1 for mean]
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∑xi2=144+225+121+324+196+256+169+289=1724.
s2=n−1∑xi2−nxˉ2=71724−8(14.5)2=71724−1682=742=6.
[3 marks: 1 for ∑x2, 1 for formula, 1 for answer]
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Var(Xˉ)=nσ2=6425≈0.391.
[2 marks: 1 for formula, 1 for answer]
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H0:μ=170; H1:μ>170.
[2 marks: 1 for H0, 1 for H1]
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Since 2.10>1.645, the test statistic falls in the critical region. Reject H0. There is sufficient evidence at the 5% level to suggest the mean height is greater than 170cm.
[3 marks: 1 for comparison, 1 for decision, 1 for context]
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- List all 2000 residents in a fixed order (e.g., alphabetical).
- Calculate interval k=2000/50=40.
- Select a random starting number between 1 and 40.
- Select every 40th resident thereafter until 50 are chosen.
[4 marks: 1 for ordering, 1 for interval, 1 for random start, 1 for process]