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Question -

How many different five-digit number license plates can be made if
(i) the first digit cannot be zero, and the repetition of digits is not allowed,
(ii) the first-digit cannot be zero, but the repetition of digits is allowed?



Answer -

(i) We know that zerocannot be the first digit of the license plates. And the repetition of digitsis not allowed.

Let us assume five boxes,now the first box can be filled with one of the nine available digits, so thepossibility is 9C1

Similarly, the secondbox can be filled with one of the nine available digits, so the possibilityis 9C1

The third box canbe filled with one of the eight available digits, so the possibility is 8C1

The fourth boxcan be filled with one of the seven available digits, so the possibilityis 7C1

The fifth box canbe filled with one of the six available digits, so the possibility is 6C1

Hence, the totalnumber of possible outcomes is 9C1 × 9C1 × 8C1 × 7C1 × 6C1 =9 × 9 × 8 × 7 × 6 = 27,216

(ii) We know thatzero cannot be the first digit of the license plates. And the repetition ofdigits is allowed.

Let us assume fiveboxes, now the first box can be filled with one of the nine available digits,so the possibility is 9C1

Similarly, the secondbox can be filled with one of the ten available digits, so the possibilityis 10C1

The third box canbe filled with one of the ten available digits, so the possibility is 10C1

The fourth boxcan be filled with one of the ten available digits, so the possibility is 10C1

The fifth box canbe filled with one of the ten available digits, so the possibility is 10C1

Hence, the totalnumber of possible outcomes is  9C1 × 10C1 × 10C1 × 10C1 × 10C1 =9 × 10 × 10 × 10 × 10 = 90,000

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