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Number System — Mathematics Questions & Practice

Practise 313 Number System questions from Mathematics for competitive exams such as UPSC, Banking, SSC and Railway. Read the worked questions below, check every answer with an explanation, and track what you get wrong.

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Practice questions on Number System — with answers

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1. What is the sum of the first 25 natural numbers?

A315
B320
C325
D330

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Answer: C

Sum of first n natural numbers = n(n+1)/2 = 25x26/2 = 325.

2. What is the sum of the first 50 natural numbers?

A1175
B1250
C1275
D1300

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Answer: C

Sum of first n natural numbers = n(n+1)/2 = 50x51/2 = 1275.

3. Which of the following is a prime number?

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Answer: B

17 is a prime number, divisible only by 1 and itself; 21, 33, and 51 are composite.

4. What is the smallest prime number?

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Answer: C

2 is the smallest prime number and the only even prime number.

5. What is the smallest number that must be added to 1780 to make it exactly divisible by 13?

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Answer: A

1780 ÷ 13 gives remainder 9 (13×136=1768, 1780-1768=12; recompute: 13×137=1781, so 1780 needs 1 more... checking carefully: 13×136=1768, remainder=12, so we need 13-12=1). Correct calculation: 1780/13 = 136.9..., 13×136=1768, 1780-1768=12, so add 13-12=1.

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Number System — Mathematics Questions & Practice

Practice questions on Number System — with answers

1. What is the sum of the first 25 natural numbers?

2. What is the sum of the first 50 natural numbers?

3. Which of the following is a prime number?

4. What is the smallest prime number?

5. What is the smallest number that must be added to 1780 to make it exactly divisible by 13?

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