9514 1404 393
Answer:
The principal was right. The numbers don't add up.
Step-by-step explanation:
Based on the categorization, the total number of students polled is ...
290 +300 +270 -80 -70 -60 -2(50) = 550
The number reportedly polled is 500, so the numbers given are inconsistent.
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Here's how we understand the categorization.
N(laptop) = N(all three) +N(laptop & tablet) +N(laptop & desktop) +N(laptop only)
N(tablet) = N(all three) +N(laptop & tablet) +N(desktop & tablet) +N(tablet only)
N(desktop) = N(all three) +N(laptop & desktop) +N(desktop & tablet) +N(desktop only)
Then the sum N(laptop) +N(tablet) +N(desktop) is ...
N(L) +N(T) +N(D) = 3N(ltd) +2N(lt) +2N(ld) +2N(td) +N(l) +N(t) +N(d)
where N(L) = number owning a laptop, and N(l) = number owning a laptop only.
