Answer:
520 girls attended the picnic
Explanation:
Hello
step 1
Let
Homewood middle school total students=1200
A=unknown=total of girls
(2/3)A=total girls attended the picnic
B=unknown= total of boys
(1/2)B=total boys attended the picnic
step2
replace

Step 3
find A and B
from equation (1)

from equation (2)

total girls attended the picnic=(2/3)A=(2/3)780=520
520 girls attended the picnic