Student Marks Range Optimization

CAT 2022 Slot 2 · QA · Hard · Arithmetic

Five students, including Amit, appear for an examination in which possible marks are integers between 0 and 50, both inclusive. The average marks for all the students is 38 and exactly three students got more than 32. If no two students got the same marks and Amit got the least marks among the five students, then the difference between the highest and lowest possible marks of Amit is

  1. A.

    21

  2. B.

    24

  3. C.

    20

  4. D.

    22

Answer

C

Explanation

Let marks of 5 students in ascending order be A<S2<S3<S4<S5A < S_2 < S_3 < S_4 < S_5. Total marks = 5×38=1905 \times 38 = 190. Exactly 3 students got >32> 32, so S3,S4,S5>32S_3, S_4, S_5 > 32, which means S333S_3 \ge 33. And A,S232A, S_2 \le 32.

To find highest possible value of AA: To maximize AA, we should minimize S5,S4,S3S_5, S_4, S_3 and make S2S_2 close to AA. Min values for S3,S4,S5S_3, S_4, S_5 with distinct integers >32> 32 are 33, 34, 35. So A+S2+33+34+35=190    A+S2=88A + S_2 + 33 + 34 + 35 = 190 \implies A + S_2 = 88. Since S232S_2 \le 32, A=88S28832=56A = 88 - S_2 \ge 88 - 32 = 56, which exceeds 32 (contradiction). So S2S_2 can be at most 32. But A<S232A < S_2 \le 32. Wait, to maximize AA, we make S5=50,S4=49,S3=48S_5 = 50, S_4 = 49, S_3 = 48? No, to maximize AA, we MINIMIZE S3,S4,S5S_3, S_4, S_5. Min S3,S4,S5S_3, S_4, S_5: if S3=33,S4=34,S5=35S_3=33, S_4=34, S_5=35, sum = 102. A+S2=88A + S_2 = 88. Since A<S232A < S_2 \le 32, A+S231+32=63<88A + S_2 \le 31 + 32 = 63 < 88. So S3,S4,S5S_3, S_4, S_5 must sum to MORE to leave a smaller sum for A+S2A + S_2. To get A+S263A + S_2 \le 63, sum of S3+S4+S519063=127S_3+S_4+S_5 \ge 190 - 63 = 127. To maximize AA, we set S2=32S_2 = 32, then A+32=190(S3+S4+S5)A + 32 = 190 - (S_3+S_4+S_5). To maximize AA, we minimize S3+S4+S5S_3+S_4+S_5 subject to A+S263A + S_2 \le 63. A+S2=190(50+49+48)=190147=43A + S_2 = 190 - (50 + 49 + 48) = 190 - 147 = 43. With S2=32S_2 = 32, A=4332=11A = 43 - 32 = 11. Wait, if S5=50,S4=49,S3=33S_5=50, S_4=49, S_3=33, sum = 132     A+S2=58\implies A+S_2 = 58. If S2=32,A=26S_2 = 32, A = 26. Check if A=26,S2=32,S3=33,S4=49,S5=50A=26, S_2=32, S_3=33, S_4=49, S_5=50: sum = 26+32+33+49+50=19026+32+33+49+50 = 190. All conditions met! So Max A=26A = 26.

To minimize AA: Maximize S2,S3,S4,S5S_2, S_3, S_4, S_5. Max S5=50,S4=49,S3=48,S2=32S_5=50, S_4=49, S_3=48, S_2=32. Sum = 50+49+48+32=17950+49+48+32 = 179. Then Min A=190179=6A = 190 - 179 = 6 or check S2<32S_2 < 32 giving even smaller AA. Wait, A0A \ge 0, but if A=6,S2=32,S3=48,S4=49,S5=50A=6, S_2=32, S_3=48, S_4=49, S_5=50, sum = 190. Max AMin A=266=20A - \text{Min } A = 26 - 6 = 20.

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