1. **State the problem:** We want to find the probability that a student pilot passes the written test before the fourth try, given the probability of passing on any single try is $0.7$. 2. **Understand the problem:** "Before the fourth try" means the student passes on the 1st, 2nd, or 3rd attempt. 3. **Calculate the probability of passing on each try:** - Probability of passing on the 1st try: $0.7$ - Probability of failing the 1st try and passing on the 2nd try: $(1 - 0.7) \times 0.7 = 0.3 \times 0.7 = 0.21$ - Probability of failing the first two tries and passing on the 3rd try: $(1 - 0.7)^2 \times 0.7 = 0.3^2 \times 0.7 = 0.09 \times 0.7 = 0.063$ 4. **Sum these probabilities:** $$ P(\text{pass before 4th try}) = 0.7 + 0.21 + 0.063 = 0.973 $$ 5. **Conclusion:** The probability that the student passes before the fourth try is $0.973$. **Answer: c. 0.973**