Question 843499: of the people in the class, 15 can spell parallel, 14 can spell pythagoras, 5 can spell both words and 4 can spell neither. How many pupils are there in the class?
Found 2 solutions by ewatrrr, Theo:
Answer by ewatrrr(24785)   (Show Source):
You can put this solution on YOUR website!
Hi,
15 can spell parallel, 14 can spell pythagoras,
5 can spell both words and 4 can spell neither
(15-5) + (14-5) + 5 + 4 = 28 people in the class.
Answer by Theo(13342)  (Show Source):
You can put this solution on YOUR website! i believe your answer will be 28.
number of people who can spell parallel = 15
number of people who can spell pythagoras = 14
number of people who can spell both = 5
number of people who can spell neither = 4
the number of people who can spell both are being counted in the number of people who can spell parallel and also being counted in the number of people who can spell pythagoras.
because of this, they are being counted twice, so you have to subtract their number from the total to get everything else in order.
you will get the total = 15 + 14 - 5 + 4
now you have completely separate categories with no double counting.
you have spell parallel DISABLED_event_only= 10
you have spell pythagoras DISABLED_event_only= 9
you have spell both = 5
you have spell neither = 4
the total is therefore equal to 28 which is the number of people in the class.
consider:
letters in set 1 = ab
letters in set 2 = bc
letters in both set 1 and set 2 = b
if you just count the number of letters in set 1 and set 2, you will get 4 letters.
however, the letter b is in both set 1 and set 2 so it is being counted twice.
you therefore have to subtract 1 from the total to get the total right.
the total letters in set a or b is equal to 3.
it is equal to the letter a, the letter b, and the letter c.
the 3 sets are:
letters in set 1 DISABLED_event_only= a
letters in set 2 DISABLED_event_only= c
letters in both set 1 and set 2 = b
the total of 3 is correct.
the total of 4 would have been wrong because the letter b was being counted twice.
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