Probability Interest Growth
1. **Stating the problem:** We want to find two probabilities related to significant earnings growth and interest rates changes in 2025:
(a) The overall probability of significant earnings growth.
(b) Given significant earnings growth, the probability that interest rates will be more than 1% lower than this year.
2. **Define events:**
- Let $H$ = interest rates more than 1% higher than this year in 2025.
- Let $L$ = interest rates more than 1% lower than this year in 2025.
- Let $M$ = interest rates within 1% of this year's rates.
- Let $G$ = significant earnings growth.
3. **Given probabilities:**
- $P(H) = 0.03$
- $P(L) = 0.85$
- $P(M) = 1 - P(H) - P(L) = 1 - 0.03 - 0.85 = 0.12$
- $P(G|H) = 0.1$
- $P(G|L) = 0.8$
- $P(G|M) = 0.5$
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4. **(a) Calculate** $P(G)$, the total probability of significant earnings growth, using the Law of Total Probability:
$$
P(G) = P(G|H)P(H) + P(G|L)P(L) + P(G|M)P(M)
$$
$$
= (0.1)(0.03) + (0.8)(0.85) + (0.5)(0.12)
$$
$$
= 0.003 + 0.68 + 0.06 = 0.743
$$
5. **(b) Calculate** $P(L|G)$, the probability that interest rates are more than 1% lower given significant growth. Use Bayes' theorem:
$$
P(L|G) = \frac{P(G|L)P(L)}{P(G)}
$$
$$
= \frac{(0.8)(0.85)}{0.743} = \frac{0.68}{0.743} \approx 0.915
$$
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**Final answers:**
- (a) The probability of significant earnings growth is **$0.743$**.
- (b) Given significant growth, the probability interest rates are more than 1% lower is approximately **$0.915$**.