Question 12

Mathematics Basic Algebra Medium

Among the given numbers below, the smallest number which, when divided by 9, 10, 15, and 20, leaves the remainders 4, 5, 10, and 15 respectively is:

(A) 85
(B) 265
(C) 535
(D) 355
View Dynamic Solution & Explanation
Correct Solution: Option D

Step-by-step Solution:

We are given a number \( N \) that, when divided by 9, 10, 15, and 20, leaves remainders of 4, 5, 10, and 4, respectively. This can be expressed as: \[ N \equiv 4 \pmod{9}, \quad N \equiv 5 \pmod{10}, \quad N \equiv 10 \pmod{15}, \quad N \equiv 4 \pmod{20}. \] To find the smallest possible \( N \), we first find the least common multiple (LCM) of the divisors 9, 10, 15, and 20. The LCM is calculated as: \[ \text{LCM}(9, 10, 15, 20) = \text{LCM}(9, 5, 4) = 180. \] Now, the number \( N \) can be expressed in the form: \[ N = 180n - 5. \] Substituting \( n = 2 \) gives: \[ N = 180 \times 2 - 5 = 360 - 5 = 355. \] Thus, the number is 355.