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Each of 7474 students in a class studies at least one of the three subjects H,EH, E and PP. Ten students study all three subjects, while twenty study HH and EE , but not PP . Every student who studies PP also studies HH or EE or both. If the number of students studying HH equals that studying EE, then the number of students studying HH is

Entered answer:

Solution

✅ Correct Answer: 52

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: hh

Students studying only E: ee

Students studying only P: 00 (explained above)

Students studying H and E only (not P): 2020 (given)

Students studying H and P only (not E): xx

Students studying E and P only (not H): yy

Students studying all three: 1010 (given)


Total students equation:

h+e+0+20+x+y+10=74h + e + 0 + 20 + x + y + 10 = 74

Simplifying: h+e+x+y=44h + e + x + y = 44 ... (1)

Equal numbers studying H and E:

Students studying H = h+x+20+10=h+x+30h + x + 20 + 10 = h + x + 30

Students studying E = e+y+20+10=e+y+30e + y + 20 + 10 = e + y + 30

Since these are equal: h+x+30=e+y+30h + x + 30 = e + y + 30

Therefore: h+x=e+yh + x = e + y ... (2)


From equation (2): e+y=h+xe + y = h + x

Substituting this into equation (1):

h+(h+x)+x=44h + (h + x) + x = 44

2h+2x=442h + 2x = 44

h+x=22h + x = 22


Number of students studying H = h+x+20+10=22+20+10=52h + x + 20 + 10 = 22 + 20 + 10 = 52

Why this method works: By using the constraint that equal numbers study H and E, we can reduce our system to just one unknown (h+x)(h + x), making the problem much simpler to solve.

The answer is 52 students study subject H.

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