JEE MainMathematicsFunctionsMCQ+4 / −1
Let and . Then the number of many-one functions such that is equal to :
- A151
- B139
- C163
- D127
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Correct answer: A
- We need the number of many-one functions such that , where
Here, many-one means the function is not one-one.
- First count all functions from to such that .
Since and , total number of functions from to is
Now exclude those functions whose image does not contain . Then each element of can map only to , so number of such functions is
Hence, number of functions with is
- Among these, subtract the one-one functions, because we want many-one functions.
A one-one function from a 4-element set to a 4-element set is actually a bijection. For a bijection to satisfy is automatic, since every element of appears exactly once.
Number of one-one functions from to is
-
Therefore, required number of many-one functions is
-
Option check:
- A: ✅
- B:
- C:
- D:
So the correct option is A.
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