A student answered 12 problems on a test correctly and received a grade of 80% how many problems were on a test if all the problems were worth the same number of points

Some boys and girls were asked if they had a pet. one third of the group were boys. there were 20 boys. 20% of the girls had a pet. boys with a pet : girls with a pet = 1 : 5 i need to know how many girls there are.

Ibeg you to me 20. a reaction produces 4.93 l of oxygen, but was supposed to produce 1 mol of oxygen. what is the percent yield?

The measurement of one angle of a right triangle is 42° what is the measurement of the third angle? (there is no picture)