Question

In a school 50% of the students are younger than 10, 1/20 are 10 years old and 1/10 are older than 10 but younger than 12, the remaining 70 students are 12 years or older. How many students are 10 years old?

Answer 1

we know that
students that are younger than 10--------------------------------------------------> 50%
students that are 10 years old-------> 1/20----> 0.05-----------------------------> 5%
students that are older than 10 but younger than 12----> 1/10---> 0.10----> 10%
--------------------------------------------------------------------------------------------------------------
total of 65%
remaining=100%-65%-----> 35%
the remaining 70 students are 12 years or older
so
35%=70 students

by proportion
70/35%=x/100%-----> x=100*70/35-----> x=200 students
total students=200

students that are 10 years old-------> 0.05*200-----> 10 students

the answer is
10 students