There are a number of chocolates in a bag. If they are equally divided among…

2024

There are a number of chocolates in a bag. If they are equally divided among 14 children, 10 chocolates are left over. If they are equally divided among 15 children, 8 chocolates are left over. This condition is also satisfied if any multiple of 210 chocolates is added to the bag. What is the remainder when the minimum feasible number of chocolates in the bag is divided by 9?

  1. A.

    5

  2. B.

    10

  3. C.

    11

  4. D.

    15

Attempted by 3 students.

Show answer & explanation

Correct answer: A

Concept: When a number leaves fixed remainders on division by two different divisors, every valid number differs from the smallest such number by a multiple of their LCM -- here LCM(14, 15) = 210. When a problem explicitly states that a multiple of this LCM has been added into the total, the quantity being asked about is the smallest number in that already-incremented sequence, not the bare minimum satisfying the congruences alone.

  1. Let n be the number of chocolates. Dividing by 14 with remainder 10 means n = 14a + 10 for some whole-number a.

  2. Substitute this into the second condition (n leaves remainder 8 on division by 15): 14a + 10 is congruent to 8 modulo 15, i.e., 14a is congruent to -2 modulo 15. Since 14 is congruent to -1 modulo 15, this simplifies to -a congruent to -2 modulo 15, i.e., a is congruent to 2 modulo 15.

  3. So a = 15b + 2 for some whole number b, giving n = 14(15b + 2) + 10 = 210b + 38.

  4. The smallest whole number satisfying both remainder conditions on their own is obtained at b = 0: n = 38.

  5. However, the question tells us that the bag's actual count is obtained by adding some multiple of 210 chocolates on top of a valid base count -- so the bag itself is not simply 38, but 38 increased by one such multiple (b = 1 instead of b = 0): n = 210(1) + 38 = 248.

  6. Divide 248 by 9: 9 x 27 = 243, so 248 = 9 x 27 + 5. The remainder is 5.

Cross-check: 248 divided by 14 gives 14 x 17 = 238, remainder 10 -- matches the first condition. 248 divided by 15 gives 15 x 16 = 240, remainder 8 -- matches the second condition. And 248 divided by 9 independently gives remainder 5, confirming the result.

So the remainder when the minimum feasible number of chocolates is divided by 9 is 5.

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