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# Principle of Inclusion and Exclusion

Count to 100. How many of those numbers are odd or multiples of 5? Since 50 are odd and 20 are multiples of 5, at first glance the answer is 70...

# Principle of Inclusion and Exclusion: Level 2 Challenges

Martin's class has 40 students who took an examination in History and Mathematics. The teacher announced that 28 of them passed in Mathematics, 29 of them passed in History, and 20 of them passed in both subjects.

How many students failed both subjects?

In a higher secondary examination 80% of the examinees have passed in English and 85% in Mathematics, while 75% passed in both English and Mathematics. If 45 candidates failed in both the subjects, find the total number of candidates.

Find the sum of all natural numbers from 1 through 1000 which are neither divisible by 5 nor by 2.

The name of the 5 oceans of earth are written on 5 adhesive labels. John has to locate each ocean on a large world map. In how many ways can he get all 5 wrong?

At the Winter Sochi Olympics Press Conference, there are $$200$$ foreign journalists. Out of them,

$$175$$ people can speak German,
$$150$$ people can speak French,
$$180$$ people can speak English,
$$160$$ people can speak Japanese.

What is the minimum number of foreigners that can speak all the four languages?

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