Question

Сергей забыл пин код своего мобильного телефона , который состоит из четырех цифр . Правда, он помнит, что последняя цифра кода 0, 2 или 4...а две первые цифры нечетные. сколько существует вариантов такого пин кода?

Answer 1

На первые два места можно поставить цифры 5-ю вариантами(1, 3, 5, 7, 9), на 3-е 10 вариантов(0-9), на 4-ое - 3 варианта(0,2,4). 5*5*10*3=750

Answer 2

Number of Possible PIN Codes

To determine the number of possible PIN codes that Sergey could have for his mobile phone, we need to consider the given information. Sergey's PIN code consists of four digits, and the last digit can be either 0, 2, or 4. Additionally, the first two digits are odd.

To calculate the number of possible PIN codes, we can break down the problem into three parts:

1. The first digit: Since the first digit must be odd, there are five possible options (1, 3, 5, 7, or 9).

2. The second digit: Again, the second digit must be odd, so there are five possible options (1, 3, 5, 7, or 9).

3. The third and fourth digits: The last digit can be 0, 2, or 4, which gives us three options. Similarly, the second-to-last digit can also be 0, 2, or 4, giving us three options. Therefore, there are a total of nine possible combinations for the third and fourth digits.

To find the total number of possible PIN codes, we multiply the number of options for each part together:

Total number of possible PIN codes = (number of options for the first digit) × (number of options for the second digit) × (number of options for the third and fourth digits)

Total number of possible PIN codes = 5 × 5 × 9 = 225

Therefore, there are 225 possible PIN codes that satisfy the given conditions.