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A Level H1 Mathematics Practice Paper 5

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TuitionGoWhere Practice Paper - Maths H1 A-Level

Answer Key and Marking Scheme Version 5 of 5

Section A: Probability and Distributions

1. (a) Let XX be the number of defective batteries in the sample. XB(20,0.05)X \sim B(20, 0.05) [1]

(b) P(X=2)=(202)(0.05)2(0.95)18P(X=2) = \binom{20}{2} (0.05)^2 (0.95)^{18} =190×0.0025×0.3972...= 190 \times 0.0025 \times 0.3972... =0.1887...= 0.1887... 0.189\approx 0.189 [2]

(c) P(X>1)=1P(X1)P(X > 1) = 1 - P(X \le 1) =1[P(X=0)+P(X=1)]= 1 - [P(X=0) + P(X=1)] P(X=0)=(0.95)200.3585P(X=0) = (0.95)^{20} \approx 0.3585 P(X=1)=20(0.05)(0.95)190.3774P(X=1) = 20(0.05)(0.95)^{19} \approx 0.3774 P(X>1)=1(0.3585+0.3774)=10.7359=0.2641P(X > 1) = 1 - (0.3585 + 0.3774) = 1 - 0.7359 = 0.2641 0.264\approx 0.264 [2]

2. (a) Tree Diagram:

  • Stage 1: Branches F (0.6), M (0.4)
  • Stage 2 (from F): Branches F (0.6), M (0.4)
  • Stage 2 (from M): Branches F (0.6), M (0.4)
  • Labels must include probabilities. [2]

(b) Let YY be the number of females. YB(8,0.6)Y \sim B(8, 0.6). P(Y5)=P(Y=5)+P(Y=6)+P(Y=7)+P(Y=8)P(Y \ge 5) = P(Y=5) + P(Y=6) + P(Y=7) + P(Y=8) Using GC or formula: P(Y5)=1P(Y4)P(Y \ge 5) = 1 - P(Y \le 4) P(Y4)0.4059P(Y \le 4) \approx 0.4059 P(Y5)=10.4059=0.5941P(Y \ge 5) = 1 - 0.4059 = 0.5941 0.594\approx 0.594 [3]

3. (a) TN(45,82)T \sim N(45, 8^2). P(T<40)=P(Z<40458)=P(Z<0.625)P(T < 40) = P(Z < \frac{40-45}{8}) = P(Z < -0.625) Using GC: 0.266\approx 0.266 [2]

(b) P(T>k)=0.15P(T<k)=0.85P(T > k) = 0.15 \Rightarrow P(T < k) = 0.85 Using inverse normal: k=invNorm(0.85,45,8)k = \text{invNorm}(0.85, 45, 8) k53.29k \approx 53.29 k=53.3k = 53.3 (3 s.f.) [3]

(c) S=T1+T2+T3+T4+T5S = T_1 + T_2 + T_3 + T_4 + T_5 E(S)=5×E(T)=5×45=225E(S) = 5 \times E(T) = 5 \times 45 = 225 [1] Since independent: Var(S)=5×Var(T)=5×82=5×64=320Var(S) = 5 \times Var(T) = 5 \times 8^2 = 5 \times 64 = 320 [1]

4. (a) Check if P(AB)=P(A)P(B)P(A \cap B) = P(A)P(B). P(A)P(B)=0.4×0.5=0.2P(A)P(B) = 0.4 \times 0.5 = 0.2 Given P(AB)=0.2P(A \cap B) = 0.2. Since 0.2=0.20.2 = 0.2, events A and B are independent. [2]

(b) P(AB)=P(A)+P(B)P(AB)P(A \cup B') = P(A) + P(B') - P(A \cap B') Alternatively: P(AB)=1P(AB)P(A \cup B') = 1 - P(A' \cap B) P(AB)=P(B)P(AB)=0.50.2=0.3P(A' \cap B) = P(B) - P(A \cap B) = 0.5 - 0.2 = 0.3 P(AB)=10.3=0.7P(A \cup B') = 1 - 0.3 = 0.7 OR P(B)=10.5=0.5P(B') = 1 - 0.5 = 0.5 Since independent, P(AB)=P(A)P(B)=0.4×0.5=0.2P(A \cap B') = P(A)P(B') = 0.4 \times 0.5 = 0.2 P(AB)=0.4+0.50.2=0.7P(A \cup B') = 0.4 + 0.5 - 0.2 = 0.7 [3]


Section B: Sampling and Estimation

5. (a) The sample is a convenience sample, not random. It only includes men visiting that specific mall at that specific time, which may not represent the general population (e.g., excludes those who work during the day, live elsewhere, or do not visit malls). [1]

(b) Assign each of the 10,000 men a unique number from 1 to 10,000. Use a random number generator to select 50 distinct numbers. Select the men corresponding to these numbers. [2]

6. (a) Unbiased estimate of mean xˉ=xn=14412=12\bar{x} = \frac{\sum x}{n} = \frac{144}{12} = 12 months. [1]

(b) Unbiased estimate of variance s2=1n1(x2(x)2n)s^2 = \frac{1}{n-1} \left( \sum x^2 - \frac{(\sum x)^2}{n} \right) s2=111(1750144212)s^2 = \frac{1}{11} \left( 1750 - \frac{144^2}{12} \right) s2=111(17501728)s^2 = \frac{1}{11} (1750 - 1728) s2=2211=2s^2 = \frac{22}{11} = 2 [3]

7. (a) Population XN(μ,0.52)X \sim N(\mu, 0.5^2). Sample size n=25n=25. XˉN(μ,0.5225)=N(μ,0.01)\bar{X} \sim N(\mu, \frac{0.5^2}{25}) = N(\mu, 0.01) [2]

(b) We want P(μ0.1<Xˉ<μ+0.1)P(\mu - 0.1 < \bar{X} < \mu + 0.1). Standardize: Z=Xˉμ0.01=Xˉμ0.1Z = \frac{\bar{X} - \mu}{\sqrt{0.01}} = \frac{\bar{X} - \mu}{0.1} Limits: 0.10.1=1\frac{-0.1}{0.1} = -1 and 0.10.1=1\frac{0.1}{0.1} = 1. P(1<Z<1)=P(Z<1)P(Z<1)P(-1 < Z < 1) = P(Z < 1) - P(Z < -1) Using GC: 0.84130.1587=0.6826\approx 0.8413 - 0.1587 = 0.6826 0.683\approx 0.683 [3]

(c) As nn increases, the variance of Xˉ\bar{X} decreases (σ2n\frac{\sigma^2}{n}). The distribution becomes narrower/tighter around μ\mu. Therefore, the probability that Xˉ\bar{X} is within a fixed distance of μ\mu increases. [1]

8. (a) The sample size n=80n=80 is large (>30>30). By the Central Limit Theorem, the sampling distribution of the sample mean is approximately normal, regardless of the population distribution. [1]

(b) xˉ=52.4\bar{x} = 52.4, s2=16.9s=16.94.11s^2 = 16.9 \Rightarrow s = \sqrt{16.9} \approx 4.11. Standard Error SE=sn=4.11800.4595SE = \frac{s}{\sqrt{n}} = \frac{4.11}{\sqrt{80}} \approx 0.4595. 95% CI: xˉ±z×SE\bar{x} \pm z \times SE 52.4±1.96(0.4595)52.4 \pm 1.96(0.4595) 52.4±0.900652.4 \pm 0.9006 (51.499,53.301)(51.499, 53.301) (51.5,53.3)\approx (51.5, 53.3) [4]

9. (a) Let Rˉ\bar{R} be the mean revenue over 9 days. RˉN(800,12029)=N(800,1600)\bar{R} \sim N(800, \frac{120^2}{9}) = N(800, 1600). SD = 40. P(Rˉ<750)=P(Z<75080040)=P(Z<1.25)P(\bar{R} < 750) = P(Z < \frac{750-800}{40}) = P(Z < -1.25) Using GC: 0.1056\approx 0.1056 0.106\approx 0.106 [3]

(b) Let S9S_9 be total revenue. S9=9RˉS_9 = 9\bar{R}. E(S9)=9×800=7200E(S_9) = 9 \times 800 = 7200. Var(S9)=92×Var(Rˉ)=81×1600=129600Var(S_9) = 9^2 \times Var(\bar{R}) = 81 \times 1600 = 129600. SD(S9)=129600=360SD(S_9) = \sqrt{129600} = 360. Alternatively: Var(S9)=9×Var(R)=9×1202=129600Var(S_9) = 9 \times Var(R) = 9 \times 120^2 = 129600. P(S9>7500)=P(Z>75007200360)=P(Z>300360)=P(Z>0.8333)P(S_9 > 7500) = P(Z > \frac{7500-7200}{360}) = P(Z > \frac{300}{360}) = P(Z > 0.8333) Using GC: 0.2023\approx 0.2023 0.202\approx 0.202 [3]


Section C: Hypothesis Testing and Regression

10. (a) H0:μ=1200H_0: \mu = 1200 H1:μ<1200H_1: \mu < 1200 [2]

(b) Test statistic Z=xˉμσ/nZ = \frac{\bar{x} - \mu}{\sigma/\sqrt{n}} Z=11801200100/50=2014.1421.414Z = \frac{1180 - 1200}{100/\sqrt{50}} = \frac{-20}{14.142} \approx -1.414 Critical value for 1-tail 5% test: zcrit=1.645z_{crit} = -1.645. Since 1.414>1.645-1.414 > -1.645, the test statistic is not in the critical region. Alternatively, p-value =P(Z<1.414)0.0787= P(Z < -1.414) \approx 0.0787. Since 0.0787>0.050.0787 > 0.05, we do not reject H0H_0. Conclusion: There is insufficient evidence at the 5% level to support the claim that the mean lifetime is less than 1200 hours. [5]

11. (a) Using GC: r0.996r \approx 0.996 (3 d.p.) [2]

(b) There is a very strong positive linear correlation between advertising expenditure and monthly sales. [1]

(c) Using GC for regression line yy on xx: m4.318m \approx 4.318 c5.818c \approx 5.818 Equation: y=4.32x+5.82y = 4.32x + 5.82 (2 d.p.) [3]

(d) x=7x = 7 (since x is in $000s). y=4.318(7)+5.81836.04y = 4.318(7) + 5.818 \approx 36.04 Estimated sales: $36,040. Reliability: Reliable because x=7x=7 is within the range of the data (interpolation) and rr is close to 1. [3]

(e) x=20x=20 is well outside the range of the observed data (extrapolation). The linear relationship may not hold for such high expenditure. [1]

12. (a) Under H0H_0, XˉN(50,6236)=N(50,1)\bar{X} \sim N(50, \frac{6^2}{36}) = N(50, 1). Critical region: Xˉ<48.5\bar{X} < 48.5 or Xˉ>51.5\bar{X} > 51.5. P(Type I)=P(Xˉ<48.5)+P(Xˉ>51.5)P(\text{Type I}) = P(\bar{X} < 48.5) + P(\bar{X} > 51.5) By symmetry: 2×P(Xˉ>51.5)2 \times P(\bar{X} > 51.5) Z=51.5501=1.5Z = \frac{51.5 - 50}{1} = 1.5 P(Z>1.5)=1P(Z<1.5)10.9332=0.0668P(Z > 1.5) = 1 - P(Z < 1.5) \approx 1 - 0.9332 = 0.0668 Level of significance =2×0.0668=0.1336= 2 \times 0.0668 = 0.1336 13.4%\approx 13.4\% [4]

(b) A Type I error occurs if we reject the null hypothesis H0:μ=50H_0: \mu = 50 when the true population mean is actually 50. In this context, it means concluding the mean is different from 50 when it is actually 50. [2]

13. (a) W=WAWBW = W_A - W_B E(W)=E(WA)E(WB)=150145=5E(W) = E(W_A) - E(W_B) = 150 - 145 = 5 g [1] Since independent: Var(W)=Var(WA)+Var(WB)=25+36=61Var(W) = Var(W_A) + Var(W_B) = 25 + 36 = 61 g2^2 [1]

(b) We want P(WA>WB)P(WAWB>0)P(W>0)P(W_A > W_B) \Rightarrow P(W_A - W_B > 0) \Rightarrow P(W > 0). WN(5,61)W \sim N(5, 61). SD =617.81= \sqrt{61} \approx 7.81. P(W>0)=P(Z>057.81)=P(Z>0.640)P(W > 0) = P(Z > \frac{0 - 5}{7.81}) = P(Z > -0.640) P(Z>0.640)=P(Z<0.640)P(Z > -0.640) = P(Z < 0.640) Using GC: 0.739\approx 0.739 [3]