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Worked Examples · Example 35

Q.If B>AB > A, then which expression will have the highest value, given that AA and BB are positive integers:

a) A−BA - B
b) A×BA \times B
c) A+BA + B
d) can't say
Arunachal CbseNCERTSubjective· 1mImportance★★★★★
33% · 35/106 Questions
✓ Free question

A−BA-B is always negative, but which of A+BA+B or A×BA\times B is bigger changes with the values, so the correct choice is (d) can't say.

B>A,A,B∈Z+B > A,\quad A,B \in \mathbb{Z}^{+}

Compare the three candidate expressions A−B, A×B, A+BA-B,\ A\times B,\ A+B using test values consistent with B>AB>A.

  1. Eliminate A−BA-B. Since B>AB>A, A−B<0A-B < 0 — it is negative, hence never the greatest. Rule out (a).
  2. Compare A+BA+B and A×BA\times B with a small case. Take A=1, B=2A=1,\ B=2:
    • A−B=1−2=−1A-B = 1-2 = -1
    • A×B=1×2=2A\times B = 1\times 2 = 2
    • A+B=1+2=3A+B = 1+2 = 3 ⇒\Rightarrow here A+BA+B is greatest.
  3. Compare with a larger case. Take A=2, B=3A=2,\ B=3:
    • A−B=−1A-B = -1
    • A×B=6A\times B = 6
    • A+B=5A+B = 5 ⇒\Rightarrow here A×BA\times B is greatest.
  4. Conclusion. The greatest expression switches between A+BA+B (when A=1A=1) and A×BA\times B (when A≥2A\ge 2), so no single option is always largest.
✓Final answer

(d) Can't say. A−BA-B is always negative; the winner between A+BA+B and A×BA\times B depends on the actual positive integers.

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