Two teaching methods, A and B, are implemented for learning Spanish. There is a 70% chance of successfully learning Spanish if method A is used, and a 85% chance of success if method Bis used. However, method B is substantially more time consuming and is therefore used only 15% of the time (method A is used the other 85% of the time). The following notations are suggested:

• AMethod A is used.
• BMethod B is used.
• LSpanish was learned successfully.

A person learned Spanish successfully. What is the probability that he was taught by method A?

1. 0.85 * 0.70 = 0.5950
2. 0.70
3. (0.15 * 0.85)/(0.85 * 0.70 + 0.15 * 0.85) = 0.1765
4. (0.85 * 0.70)/(0.85 * 0.70 + 0.15 * 0.85) = 0.8235
5. (0.85 * 0.70)/(0.70 + 0.85) = 0.3839