JEE PYQ: Permutation And Combination Question 41
Question 41 - 2019 (09 Jan Shift 2)
The number of natural numbers less than 7,000 which can be formed by using the digits 0, 1, 3, 7, 9 (repetition of digits allowed) is equal to:
(1) 374
(2) 372
(3) 375
(4) 250
Show Answer
Answer: (1)
Solution
1-digit: 4. 2-digit: $4 \times 5 = 20$. 3-digit: $4 \times 5 \times 5 = 100$. 4-digit (< 7000): first digit 1, 3: $2 \times 5 \times 5 \times 5 = 250$. Total $= 4 + 20 + 100 + 250 = 374$.
BETA
