Each of students in a class studies at least one of the three subjects and . Ten students study all three subjects, while twenty study and , but not . Every student who studies also studies or or both. If the number of students studying equals that studying , then the number of students studying is
Each of students in a class studies at least one of the three subjects and . Ten students study all three subjects, while twenty study and , but not . Every student who studies also studies or or both. If the number of students studying equals that studying , then the number of students studying is
Entered answer:
Solution
We need to organize information about students studying different combinations of subjects H, E, and P using a Venn diagram approach.
Understanding what we know:
Total students = 74
10 students study all three subjects (H, E, and P)
20 students study H and E, but not P
Every student studying P also studies H or E (or both)
Number studying H = Number studying E
The key insight here is that no student studies only P because the problem states "every student who studies P also studies H or E or both."
Let us define variables for each region:
Students studying only H:
Students studying only E:
Students studying only P: (explained above)
Students studying H and E only (not P): (given)
Students studying H and P only (not E):
Students studying E and P only (not H):
Students studying all three: (given)
Total students equation:
Simplifying: ... (1)
Equal numbers studying H and E:
Students studying H =
Students studying E =
Since these are equal:
Therefore: ... (2)
From equation (2):
Substituting this into equation (1):
Number of students studying H =
Why this method works: By using the constraint that equal numbers study H and E, we can reduce our system to just one unknown , making the problem much simpler to solve.
The answer is 52 students study subject H.
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