Given: $P(E) = 0.15$

Step 1 — Use the complement rule.

An event either happens or it does not, so:

$$P(E) + P(\bar{E}) = 1$$

Step 2 — Rearrange:

$$P(\bar{E}) = 1 - P(E)$$

Step 3 — Substitute:

$$P(\bar{E}) = 1 - 0.15$$

Step 4 — Calculate:

$$\boxed{P(\bar{E}) = 0.85}$$

Check: $0.15 + 0.85 = 1$ ✔

Interpretation: The event E is fairly unlikely (a 15% chance), so its complement is quite likely (85%).

(E and $\bar{E}$ are called complementary events.)