If the ratio of boys to girls in the math class is 5:8, the total ratio of the number of boys and girls in the math class is 5+8 = <<5+8=13>>13.
The fraction that represents the number of boys in the class is 5/13, and since there are 260 students in the class, the number of boys in the class is 5/13*260 = <<5/13*260=100>>100.
The number of girls in the class is 260-100 = <<260-100=160>>160.
#### 160