2/3 of all the people who attended a certain party arrived by 8: 00 pm. how many people arrived by 8: 00 pm?
(1) 9 people arrived after 9: 00 pm.
(2) 21 people arrived between 8: 00 pm and 9: 00 pm, and by 9: 00 pm 90% of all the people who attended the party had arrived.

a) How many people who attended a certain party arrived by  8 PM           60 people

Step-by-step explanation:

2/3 of all people who attended a certain party arrived by  8 P.M . That means that  1/3  arrived in other time. But  2/3  +  1/3 is total number of people in the party.

1) 9 people arrived after 9 PM

And in 2

2) By 9 .00 PM  90 % of people were already in the party and. That means

that 9 people who arrived after are 10 %

Then if      9  people are    10 %

                 x   people are   100%

x  =  (100*9)/10      ⇒   x  =  900/10

x =  90

Here we got total number of people in the party  90

Then    2/3 of   90     is    180/3       60

1/3  0f  90      is   30