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Base Systems (Hard)

Late AMC 10/12 through early AIME — dense computation.

Base Systems: core idea

Arithmetic in base.

Example problem: hint and answer

Evaluate (243)5(243)_5 in base ten.

Hint: Expand place values or carry and borrow in the stated base. Answer: 73.

Practice (9 problems — type your answers)

  • 1. Write 100100 in base 77.

  • 2. If (3x)7=(26)8(3x)_7=(26)_8, find xx.

  • 3. Compute (123)4+(132)4(123)_4+(132)_4 in base 44.

  • 4. Find the least base b>4b>4 such that (144)b(144)_b is divisible by 55.

  • 5. Evaluate (1111)2(1111)_2 in base ten.

  • 6. Find bb if (121)b=16(121)_b=16.

  • 7. Compute (56)7−(24)7(56)_7-(24)_7 in base 77.

  • 8. Decimal 4545 is (a5)b(a5)_b. Find a+ba+b.

  • 9. Find (1234)5(mod4)(1234)_5\pmod4.

Base Systems Practice Problems — Hard