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IB Mathematics AHL 4.18 Test for proportion AI HL Paper 1- Exam Style Questions

IB Mathematics AHL 4.18 Test for proportion AI HL Paper 1- Exam Style Questions- New Syllabus

Question

At Springfield University, the weights, in kg, of 10 chinchilla rabbits and 10 sable rabbits were recorded. The aim was to find out whether chinchilla rabbits are generally heavier than sable rabbits. The results obtained are summarized in the following table.

Rabbit Weight Table

A t-test is to be performed at the 5% significance level.

(a) Write down the null and alternative hypotheses [2]

(b) Find the p-value for this test [2]

(c) Write down the conclusion to the test. Give a reason for your answer [2]

▶️ Answer/Explanation
Markscheme

(a)
\( H_0: \mu_c = \mu_s \), \( H_1: \mu_c > \mu_s \)

Define: \( \mu_c \) = mean weight of chinchilla rabbits, \( \mu_s \) = mean weight of sable rabbits
Null hypothesis: No difference in mean weights, \( \mu_c = \mu_s \)
Alternative hypothesis: Chinchilla rabbits are heavier, \( \mu_c > \mu_s \)
Test type: One-tailed

Result: \( H_0: \mu_c = \mu_s \), \( H_1: \mu_c > \mu_s \) [2]

(b)
0.041

Test: Two-sample unpaired t-test, assuming equal variances
Data: Chinchilla weights (4.9, 4.2, 4.1, 4.4, 4.3, 4.6, 4.0, 4.7, 4.5, 4.4), \( n_c = 10 \)
Sable weights (4.2, 4.1, 4.1, 4.2, 4.5, 4.4, 4.5, 3.9, 4.2, 4.0), \( n_s = 10 \)
Chinchilla mean: \( \bar{x}_c = \frac{4.9 + 4.2 + 4.1 + 4.4 + 4.3 + 4.6 + 4.0 + 4.7 + 4.5 + 4.4}{10} = 4.41 \)
Sable mean: \( \bar{x}_s = \frac{4.2 + 4.1 + 4.1 + 4.2 + 4.5 + 4.4 + 4.5 + 3.9 + 4.2 + 4.0}{10} = 4.21 \)
Chinchilla variance: \( s_c^2 \approx \frac{(4.9 – 4.41)^2 + \cdots + (4.4 – 4.41)^2}{9} \approx 0.0765333333 \)
Sable variance: \( s_s^2 \approx \frac{(4.2 – 4.21)^2 + \cdots + (4.0 – 4.21)^2}{9} \approx 0.0409888889 \)
Pooled variance: \( s_p^2 = \frac{(10 – 1) \times 0.0765333333 + (10 – 1) \times 0.0409888889}{10 + 10 – 2} \approx 0.0587611111 \)
T-statistic: \( t = \frac{4.41 – 4.21}{\sqrt{\frac{0.0587611111}{10} + \frac{0.0587611111}{10}}} \approx 1.844463643 \)
Degrees of freedom: \( df = 10 + 10 – 2 = 18 \)
P-value: \( P(T > 1.844463643, df = 18) \approx 0.0408 \)
Round to three decimal places: 0.041

Result: 0.041 [2]

(c)
Reject \( H_0 \). There is sufficient evidence to suggest that chinchilla rabbits are generally heavier than sable rabbits

Significance level: \( \alpha = 0.05 \)
P-value: 0.041
Compare: \( 0.041 < 0.05 \)
Decision: Reject \( H_0 \)
Reason: P-value is less than the significance level, indicating sufficient evidence for \( H_1 \)

Result: Reject \( H_0 \). There is sufficient evidence to suggest that chinchilla rabbits are generally heavier than sable rabbits [2]

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