Question

A star rises at 8 pm tonight. At what time will it rise after a month? Why?

Answer 1

The star will rise at 6 pm after a month. This is because each star rises or sets 4 min earlier everyday. Thus, in a month, the total advancement in the rising time of a star = $4\times 30=120\min =2\mathrm{h}$
So, if a star rises at 8 pm today, it will rise before 2 h i.e. at 6 pm after a month.