You ran an A/B test on a new rider signup prompt in the Didi Chuxing app. In the control group, 20,000 users saw the current prompt and 2,400 completed signup, while in the treatment group, 20,500 users saw the new prompt and 2,665 completed signup. Use a 5% significance level.
Is the observed increase in signup conversion statistically significant, and how would you decide whether the change is likely real rather than random variation?