Blind college in Bryan has 620 students. The difference between male and female students is 20. How many female students are there?
f + m = 620 , assuming there are more females than males, you don't say
f - m = 20
add them
2f = 640
f = 320
then m = 300
If there are more males than females, just change the 2nd equation to
m - f = 20,
It will interchange the answers.