FUNDAMENTAL PRINCIPLE OF COUNTING

FUNDAMENTAL PRINCIPLE OF COUNTING 
If an event can happen exactly m ways and following it a second event can happen in exactly in n ways, then the two events in succession can happen exactly in mn different ways
1.In a class there are 27 boys  and 14 girls. The teacher wants to select one boy and one girl to represent the class. In how many ways can the teacher make this selection?
No of ways to select boys = 27
The teacher has to perform two operations
1.selecting one from 27 boys in 27 ways
2.selecting a girl from 14 girls.
In total ways 27*14 ways
=378 ways
2) A flag contains 3 blocks with different colours. Each coloured differently. If there are 6 different colours. How many such designs are possible?
3) How many numbers are there in between 100 and 1000 such 7 is in the unit place?
4) How many three digit numbers are there with all digits distinct?
PERMUTATIONS ;
FACTORIALS, PERMUTATIONS 

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