Find equivalent from the rational number having a common denominator in each of the following collection of rational number question number 12 by 5, 6 by 30

According to modern science, earth is about 4.5 billion years old and written human history extends back about 10,000 years. suppose the entire history of earth is represented with a 10-meter-long timeline, with the birth of earth on one end and today at the other end.

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).

In priyas math class there are 10 boys and 15 girls. what is the ratio of boys to girls in priyas math class? express your answer as a decimal