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Daily · 2026-09-30

Daily math problems for September 30, 2026 — Absolute value, Calculus, Logic & more

One bite-sized math problem set for the day. Solve the 10 multiple-choice problems and reveal the worked solutions.

1 / 10
🌍 International
BeginnerAbsolute value
The sum of all real solutions of is:

Problems & worked solutions

🌍 International

Problem 1 — Algebra

The sum of all real solutions of ∣x−3∣=5∣x−3∣=5 is:

Show answer & worked solution
  1. A. 66✓ correct
  2. B. 55
  3. C. −2−2
  4. D. 88

x−3=±5x−3=±5 gives x=8x=8 or x=−2x=−2. Sum =8+(−2)=6=8+(−2)=6.

🇷🇴 RO M1

Problem 2 — Antiderivatives

∫5 dx∫5dx equals:

Show answer & worked solution
  1. A. 00
  2. B. 55
  3. C. 5x+C5x+C✓ correct
  4. D. x25+C5x2​+C

∫c dx=cx+C∫cdx=cx+C. So ∫5 dx=5x+C∫5dx=5x+C.

🇷🇴 RO M1

Problem 3 — Recursive Integrals

For In=∫01xn dxIn​=∫01​xndx, lim⁡n→∞Inlimn→∞​In​ equals:

Show answer & worked solution
  1. A. 00✓ correct
  2. B. 11
  3. C. ∞∞
  4. D. divergentdivergent

lim⁡1n+1=0limn+11​=0.

🇷🇴 RO M1

Problem 4 — Logic & Induction

Which statement is logically equivalent to "if n2n2 is even, then nn is even"?

Show answer & worked solution
  1. A. If n is even, then n2 is evenIf n is even, then n2 is even
  2. B. If n is odd, then n2 is oddIf n is odd, then n2 is odd✓ correct
  3. C. If n2 is odd, then n is evenIf n2 is odd, then n is even
  4. D. n is even if and only if n2 is oddn is even if and only if n2 is odd

The contrapositive of "n2n2 even ⇒⇒ nn even" is "nn odd ⇒⇒ n2n2 odd". A statement and its contrapositive always have the same truth value.

🇷🇴 RO M1

Problem 5 — Matrix Equations

For A=(1002)A=(10​02​) and B=(2468)B=(26​48​), solve XA=BXA=B. Then XX equals:

Show answer & worked solution
  1. A. (1234)(13​24​)
  2. B. (2434)(23​44​)
  3. C. (2264)(26​24​)✓ correct
  4. D. (2162)(26​12​)

A−1=(1001/2)A−1=(10​01/2​). So X=B⋅A−1=(2⋅14⋅1/26⋅18⋅1/2)=(2264)X=B⋅A−1=(2⋅16⋅1​4⋅1/28⋅1/2​)=(26​24​).

🇷🇴 RO M1

Problem 6 — The Unit Circle

The value of cos⁡ ⁣(−π3)cos(−3π​) is:

Show answer & worked solution
  1. A. 1221​✓ correct
  2. B. −12−21​
  3. C. 3223​​
  4. D. −32−23​​

cos⁡ ⁣(−π3)=cos⁡π3=12cos(−3π​)=cos3π​=21​.

🇷🇴 RO M1

Problem 7 — Determinants

If det⁡(A)=3det(A)=3 and det⁡(B)=−2det(B)=−2, what is det⁡(AB)det(AB)?

Show answer & worked solution
  1. A. −6−6✓ correct
  2. B. 11
  3. C. 55
  4. D. 66

det⁡(AB)=3⋅(−2)=−6det(AB)=3⋅(−2)=−6.

🇷🇴 RO M1

Problem 8 — Rings & Fields

The set of units (multiplicatively invertible elements) of Z8Z8​ is:

Show answer & worked solution
  1. A. {0^}{0^}
  2. B. {1^,2^,3^}{1^,2^,3^}
  3. C. {1^,3^,5^,7^}{1^,3^,5^,7^}✓ correct
  4. D. Z8∖{0^}Z8​∖{0^}

The units are the residues coprime to 88: {1,3,5,7}{1,3,5,7}, four elements.

🌍 International

Problem 9 — Combinatorics

The number of permutations of (1,2,3,4)(1,2,3,4) in which no element is in its original position is:

Show answer & worked solution
  1. A. 99✓ correct
  2. B. 66
  3. C. 1212
  4. D. 2424

!4=4!(1−1+12−16+124)=24⋅924=9!4=4!(1−1+21​−61​+241​)=24⋅249​=9.

🇷🇴 RO M1

Problem 10 — Conic Sections

For the ellipse x225+y29=125x2​+9y2​=1, the eccentricity equals:

Show answer & worked solution
  1. A. 3553​
  2. B. 4554​✓ correct
  3. C. 5445​
  4. D. 4334​

a=5a=5, b=3b=3, c=25−9=4c=25−9​=4. So e=45e=54​.

Practise these topics

  • Antiderivatives
  • The Unit Circle
  • Conic Sections
2026-09-29
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