1/n + 3/5 = 1

[math_celebrity]

1/n + 3/5 = 1

Subtract 3/5 from each side where 1 = 5/5
1/n + 3/5 - 3/5 = 5/5 - 3/5
1/n = 2/5

Cross multiply:
5 * 1 = 2 * n
2n = 5

Divide each side by 2:
n = 5/2 or 2.5