In a class 40% of the students take Math and 70% take Spelling. If 15% of the students take both Math and Spelling, what % of the students did not take either of the two subjects?

May 13, 2016

Only 5% of the students did not take any of 2 mentioned subjects.

Explanation:

To calculate the amount of students which did not take any of those subjects first we have to calculate the amount of the students which took at least one subject.
To do this we have to perform calculations:

$\frac{40}{100} + \frac{70}{100} - \frac{15}{100} = \frac{40 + 70 - 15}{100} = \frac{95}{100}$

The substraction comes from the fact that students which took both classes were calculated twice (once as Math students and once again as Spelling students)

Now if we have the amount of students which took at least one subject we have to substract this number from the whole class:

100%-95%=100/100-95/100=5/100