Musa is the class teacher of a class of 45 students. He wants to split them into three groups by age. If a third of the class is under 11 years, and two-fifths are above 11 but under 13, how many students will be in the third group (13 years and above)?
Use reasoning to answer the following question.
12
The first group is a third of the class which is (1 / 3) * 45 = 15 students.

There are 15 students in the first group, so there are 45 - 15 = 30 students.

The second group is two - fifths of the class which is (2 / 5) * 45 = 18 students.

There are 18 in the second group so there are 30 - 18 = 12 students left in the third group.

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The final answer: 12