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ALP Mock Test 8: Probability, Profit, Geometry & Speed Problems

Probability: Conditional Probability Formula

Question 1: Events E and F have P(E)=0.4, P(F)=0.8, P(F/E)=0.6. Find P(E/F).

Solution: Use formula P(E∩F) = P(F/E)·P(E) = P(E/F)·P(F)

  • P(E∩F) = 0.6 × 0.4 = 0.24
  • P(E/F) = 0.24 / 0.8 = 0.3

Isosceles Triangle: Ratio and Heron's Formula

Question 2: Equal sides:unequal side = 6:11, perimeter = 46 cm. Find approximate area.

  • Sides = 12, 12, 22 cm
  • Semi-perimeter s = 23 cm
  • Heron: √[23(11)(11)(1)] = √(23×121) = 11√23 ≈ 11×4.796
  • Area ≈ 53 cm² (slightly less than 55)

Profit & Discount: Successive Percentage Change

Question 3 & 5: Calculate net profit using formula x - y - xy/100. For more on profit formulas, see Profit & Loss: Solve Aptitude Problems Fast with Formulas & Tricks.

  • Q3: First pen 70% profit + 9% discount → net profit = 70 - 9 - (630/100) = 61 - 6.3 = 54.7%
  • Q5: Marked 21% profit, 12% discount → net = 21 -12 - (21×12/100) = 9 - 2.52 = 6.48%

Election & Valid Votes

Question 4: 15% didn't vote, 10% invalid among voters. Winner got 72% of valid votes = 8262.

  • Valid votes = 8262 ÷ 0.72 = 11,475

Train Speed & Bridge Length

Question 6 & 7: 220m train crosses post in 11s → speed = 20 m/s

  • Same train crosses bridge in 18s: (220 + L) / 20 = 18 → L = 140 m

Relative Speed & Time

Question 8: Train 50% faster than car, train stops 12.5 min. Distance 75 km, same arrival time.

  • Speed ratio train:car = 3:2 → time ratio = 2:3
  • Time difference = 12.5 min = 1 unit → car time = 37.5 min = 5/8 hr
  • Car speed = 75 ÷ (5/8) = 120 km/hr

Trigonometry Identity

Question 13: Given (1 - cosθ)/sinθ = 1/5, find (1 + cosθ)/sinθ

  • Identity: product = 1 → inverse = 5

Ratio: Income, Expenditure, Savings

Question 14: Income ratio (A:B) = 3:5, Expense ratio = 1:3, both save ₹10,000. For more on ratios and proportions, visit Understanding Averages, Ratios, and Proportions in Mathematics.

  • Cross-multiply: (3×3 - 5×1) = 4 units = 20,000 → 1 unit = 5,000
  • Bharat's income = 5 × 5,000 = ₹25,000

Time & Work Efficiency

Question 18: Abhi 50 days, Varun 25% more efficient (ratio 4:5). Work = 200 units.

  • Together 8 days → 9×8 = 72 done; Charu does remaining 128 in 6.4 days → efficiency 20
  • 75% of 200 = 150; Varun+Charu = 25; Days = 150/25 = 6 days

Exponents & Powers

Question 19: 4^(2x-16) × 4^(x-5) = 64 = 4³

  • Equate powers: 3x - 21 = 3 → x = 8

Concentric Circles & Triplets

Question 28: Radii 34 cm (inner) and 50 cm (outer). BC = 32 cm chord on inner circle.

  • Use 8-15-17 and 3-4-5 triplets
  • Distance from center to BC = 30 cm
  • Half chord on outer = 40 cm → full AD = 80 cm

Quadratic Roots

Question 25: Roots -1 and -2 satisfy 3x² + px + q = 0

  • Substitute → p - q = 3 and 2p - q = 12 → p = 9, q = 6
  • 3p - 2q = 27 - 12 = 15

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