Fifty percent of all the students attending a school on a certain day arrived by 7:00 AM. How many students arrived by 7:00 AM on that day?

(1) Fifteen students arrived between 7:00 AM and 8:00 AM, and 4/5 of that day’s total attending students arrived by 8:00 AM.
\(\frac{4}{5}\) means \(\frac{4}{5}*100=80%\) arrive by 8:00 AM. but fifteen students arrived between 7:00 AM and 8:00 AM.
Also, fifty percent of all the students attending a school on a certain day arrived by 7:00 AM, so 80%-50%=30%=15....100%=\(\frac{15}{30}*100=50\).
thus 50% or 25 students attending a school on a certain day arrived by 7:00 AM.

(2) Ten students arrived after 8:00 AM that day.
insuff

A

Fifty percent of all the students attending a school on a certain day arrived by 7:00 AM. How many students arrived by 7:00 AM on that day?

(1) Fifteen students arrived between 7:00 AM and 8:00 AM, and 4/5 of that day’s total attending students arrived by 8:00 AM.

(2) Ten students arrived after 8:00 AM that day

From question stem, 50% students arrive by 7:00 AM. We have to find out the number of students who arrive by 7:00 AM.

(1) (4/5 - 1/2) = 3/10 of total students come between 7:00 AM and 8:00 AM. From this we can find out total number of students and students who arrive by 7:00 AM.SUFFICIENT.

(2) We don't know what percentage of total students these 10 students is, so NOT SUFFICIENT.

A is the answer.

Can someone explain the language of the following:
"Fifteen students arrived between 7:00 AM and 8:00 AM, and 4/5 of that day’s total attending students arrived by 8:00 AM". as a non-native speaker, it looks for me as odd sentence and I understand that 50% attended by 7 a.m. then 15 students attended between 7 & 8 a.m. then another 4/5 of total students ( who attended that day) attended by 8 a.m. which is not rational?