A class has 30 boys and 20 girls. The average age of boys is 11 yrs and girls 12 What is the
average age of the whole class."

x = total age of boys

x / 30 = 11yrs

Multiply both sides by 30

x = 330

y = total age of girls

y / 20 = 12

Multiply both sides by 20

y = 240

(240 + 330) / 50 = 11.4 yrs

The average age of the whole class = 11.4 years.

answer: all of the odd numbers were opened

the first person was the one that was opening all of the lockers. since one is odd, this causes all of the odd number lockers to be opened in the end.