Molly has received scores of 85, 88, 87, and 90 on her algebra tests. What is the minimum score she must receive on the fifth test to have an overall test score average of at least 87?

1) Find the medium for the first 4 numbers

85 + 88 + 87 + 90 = 350

350 : 4 = 87.5

2) Try out different numbers

85 + 88 + 87 + 90 + x = 435

450 : 5 = 90

x = ?

85 + 88 + 87 + 90 + 85 = 435

x = 85

Therefore, the answer is 85.