A gardener plants 600 seeds of a made-up variety, a random sample from a large batch, and 150 of…

Step 1. Conditions. The seeds are a random sample. There are $150$ successes and $450$ failures, both at least $10$. The batch is large.

Step 2. Standard error. $\sqrt{\dfrac{0.25 \times 0.75}{600}} \approx 0.0177$.

Step 3. Margin. $1.96 \times 0.0177 \approx 0.0346$.

Step 4. Interval. From $0.25 - 0.0346 \approx 0.215$ to $0.25 + 0.0346 \approx 0.285$.