Optimization with Constraints

MAT 2018 · Mathematical Skills · Medium · Word Problems

I went to a shop to purchase some refills costing Rs. 1.601.60 each but the clerk did not have change for my 2020-rupee note. I was constrained to purchase some 3030 paise labels as well so that no money needed to be returned. After purchasing the maximum number of refills under the given constraints, how many labels did I have to purchase?

  1. A.

    2

  2. B.

    4

  3. C.

    6

  4. D.

    8

Answer

D

Explanation

Let rr be the number of refills and ll be the number of labels. 160r+30l=2000160r + 30l = 2000 Dividing by 10: 16r+3l=20016r + 3l = 200.

We want to maximize rr. The maximum possible value for r≤⌊200/16⌋=12r \le \lfloor 200/16 \rfloor = 12.

  • If r=12r = 12: 16(12)=19216(12) = 192, remaining =8= 8, which is not divisible by 3.
  • If r=11r = 11: 16(11)=17616(11) = 176, remaining =24= 24, which is divisible by 3 (24/3=824 / 3 = 8).

Thus, r=11r = 11 and l=8l = 8.

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