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A number when divided successively by 4 and 5 leaves remainders 1 and 4 respectively. What is the least such number?

  • A.17
  • B.21
  • C.37
  • D.53

Answer: A

Correct answer: 17

Successive division means the quotient from the first division is what gets divided next. Write \(N = 4x + 1\), where \(x\) is the first quotient, and then \(x = 5y + 4\).

The least value of \(N\) comes from the smallest admissible \(y\), which is \(y = 0\). That gives \(x = 4\) and

\[N = 4\times 4 + 1 = 17\]

Checking against the conditions: \(17 \div 4\) gives quotient 4 and remainder 1, and dividing that quotient, \(4 \div 5\) gives quotient 0 and remainder 4. Both requirements hold, so 17 is the least such number.

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