In a Class of 120 students numbered 1 to 120, all even numbered students opt for Physics , those whose numbers are divisible by 5 opt for Chemistry and those whose numbers are divisible by 7 opt for Math. How many opt for none of the three subject ?
Created: 4 years ago |
Updated: 2 years ago
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Physics takes = 120/2 = 60
Chemistry takes = 120/5 = 24
Mathematics takes = 120/7 = 17
Physics and chemistry = 120/10 = 12
Physics andmathematics = 120/14 = 8
Chemistry and mathematics = 120/35 = 3
Physics, Chemistry and mathematics = 120/70 = 1
So, Only physics and chemistry = 12 - 1 = 11
Only physics and mathematics = 8 - 1 = 7
Only Chemistry and mathematics = 3 - 1 = 2
Now, Only physics = 60 - 11 - 7 = 41
Only Chemistry = 24 - 11 - 2 - 1 = 10
Only mathematics = 17 - 7 - 2 - 1 = 7
Shortcut not taken none ofthe three = 120 - (41 + 10 + 7 + 11 + 7 + 2 + 1) = 12 - 79 = 41
Md Azizur Rahman
Founder of Satt
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