Class 10r sat a test. the mean mark of the class was 70%. there are 30 students in class 10r, 20 of whom are boys. the mean mark for the boys in the test was 62%.work out the mean mark for the girls.

Astuntman jumping off a 20-m-high building is modeled by the equation h=20-5t^2, where t is the same in seconds. a high-speed camera is ready to film him between 15m and 10m above the ground. for which interval of time should the camera film him?