Step-by-step explanation:
they start 5 minutes earlier.
and end 15 minutes earlier.
that means their school day is now 15-5 = 10 minutes shorter than before.
originally their school day was from 9:00 am to 3:20 pm.
that was 6 hours and 5 minutes :
6×60 + 5 = 360 + 5 = 365 minutes.
so,
365 minutes = 100%
1% = 100%/100 = 365/100 = 3.65 minutes
how many % are 10 minutes ? well, as many as times 1% fits into 10 minutes :
10/3.65 = 2.739726027...% ≈ 2.74%
they reduced the school day by about 2.74%.
