Shared Based paymants

In working share based payment questions, I found that there are two ways of calculating share base payments.

1. The actual employees leave is added with the estimate amount of employees that will leave. E.g.
100 share options priced at $10 for 500 employees over a three year period, 20 employees left during in the first year and 25% was expected to leave in that year.
Answer: 100*(500-(500*25%)-20)*$10*(1/3) = 118,333

2. Only the estimated amount of employees to leave is accounted for. E.g. 100 shares options priced at $10 for 400 employees over a three year period, 20 employees left during in the first year and 25% was expected to leave in that year.
Answer: 100*(400*(1-25%))*$10*(1/3) = $100,000

Why is there two different methods for very similar questions? What am I missing?