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In a survey of college students, $100$ had taken Cryptography, $60$ had taken Python Programming course,

$60$ had taken Computer Math Fundamentals course, $30$ had taken Cryptography and Python, $25$ had

taken Cryptography and Computer Math Fundamentals, $35$ had taken Python and Computer Math Fundamentals,

and $10$ had taken all the three courses.

Use Venn Diagram to answer the following questions.

a$.$ How many students had taken one of the above courses only?

b$.$ If $3$ students didn't take any course, how many students were surveyed?