**Answer:**

90

**Step-by-step explanation:**

Let g and b represent the number of girls and boys attending, respectively.

After 15 girls left, the ratio of boys to girls was ...

b/(g -15) = 2/1

b = 2g -30 . . . . . multiply by (g-15)

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After 45 boys left, the ratio of girls to boys was ...

(g -15)/(b -45) = 5/1

g -15 = 5b -225 . . . . . . multiply by (b-45)

g = 5b -210

Using the latter to substitute into the former, we have ...

b = 2(5b -210) -30

450 = 9b . . . . . add 450-b

50 = b . . . . . . 50 boys attended

g = 5(50) -210 = 40 . . . . . 40 girls attended

**The number of students who attended the party was 50 +40 = 90**.

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<em>Check</em>

After 15 girls left, the ratio of boys to girls was 50/25 = 2/1.

After 45 boys left, the ratio of girls to boys was 25/5 = 5/1.