Q.

The number of 3 digited numbers 'abc' such that b<c is 

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a

450

b

405

c

400

d

410

answer is B.

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Detailed Solution

Let a, b, c be the required 3 digits

Number ‘a’ can be selected from 1 to 9

In 9 ways.

For b,c select 2 digits from 0 to 9 in 10C2 ways.

They can be arranged in ascending order in one way once b<c

No.of 3 digit numbers = 9× 10C2                                              =9×45=405

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