What is the LCM of 45 and 105?
- A4725
- B157.5
- C315
- D630
Show answer
Answer: (C) 315
LCM = HCF × 3 × 7 = 315.
ISRO Scientist Number System Questions with Answers & Explanations
20 Number System questions from the Quantitative Aptitude section of ISRO Scientist, each with the correct answer and a worked explanation. Try each question first, then tap Show answer to check. When you're ready, take the timed chapter-wise test to see your all-India rank.
What is the unit digit of 9^96?
- A8
- B1
- C2
- D4
Show answer
Answer: (B) 1
Unit digits of powers of 9 repeat in a cycle of 4; 96 mod 4 = 0, so the unit digit is 1.
What is the value of 73² − 34²?
- A4173
- B4073
- C4212
- D1521
Show answer
Answer: (A) 4173
a² − b² = (a + b)(a − b) = 107 × 39 = 4173.
What is the LCM of 42 and 70?
- A420
- B105
- C210
- D224
Show answer
Answer: (C) 210
LCM = HCF × 3 × 5 = 210.
What is the square root of 2500?
- A49
- B52
- C51
- D50
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Answer: (D) 50
50 × 50 = 2500.
What is the sum of the first 80 natural numbers?
- A3160
- B3320
- C6400
- D3240
Show answer
Answer: (D) 3240
Sum = n(n + 1)/2 = 80 × 81/2 = 3240.
What is the remainder when 24440 is divided by 9?
- A4
- B6
- C5
- D0
Show answer
Answer: (C) 5
24440 = 9 × 2715 + 5.
What is the unit digit of 27^51?
- A9
- B3
- C7
- D0
Show answer
Answer: (B) 3
Unit digits of powers of 7 repeat in a cycle of 4; 51 mod 4 = 3, so the unit digit is 3.
What is the value of 97² − 47²?
- A7200
- B7300
- C2500
- D7100
Show answer
Answer: (A) 7200
a² − b² = (a + b)(a − b) = 144 × 50 = 7200.
What is the LCM of 27 and 45?
- A1215
- B135
- C144
- D270
Show answer
Answer: (B) 135
LCM = HCF × 3 × 5 = 135.
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Timed Quantitative Aptitude test · 15 questions · instant rank
What is the square root of 5625?
- A72
- B74
- C76
- D75
Show answer
Answer: (D) 75
75 × 75 = 5625.
What is the sum of the first 62 natural numbers?
- A3844
- B1891
- C2015
- D1953
Show answer
Answer: (D) 1953
Sum = n(n + 1)/2 = 62 × 63/2 = 1953.
What is the remainder when 79326 is divided by 9?
- A1
- B0
- C8
- D6
Show answer
Answer: (B) 0
79326 = 9 × 8814 + 0.
What is the unit digit of 17^76?
- A1
- B0
- C6
- D4
Show answer
Answer: (A) 1
Unit digits of powers of 7 repeat in a cycle of 4; 76 mod 4 = 0, so the unit digit is 1.
What is the value of 91² − 34²?
- A3249
- B7225
- C7125
- D7025
Show answer
Answer: (C) 7125
a² − b² = (a + b)(a − b) = 125 × 57 = 7125.
What is the LCM of 42 and 98?
- A294
- B588
- C4116
- D308
Show answer
Answer: (A) 294
LCM = HCF × 3 × 7 = 294.
What is the sum of the first 33 natural numbers?
- A594
- B561
- C528
- D1089
Show answer
Answer: (B) 561
Sum = n(n + 1)/2 = 33 × 34/2 = 561.
What is the unit digit of 17^94?
- A6
- B9
- C0
- D5
Show answer
Answer: (B) 9
Unit digits of powers of 7 repeat in a cycle of 4; 94 mod 4 = 2, so the unit digit is 9.
What is the square root of 6724?
- A83
- B82
- C84
- D79
Show answer
Answer: (B) 82
82 × 82 = 6724.
What is the HCF of 24 and 30?
- A6
- B12
- C3
- D20
Show answer
Answer: (A) 6
24 = 6 × 4 and 30 = 6 × 5, so HCF = 6.
These are RankerClub practice questions written in the ISRO Scientist pattern. They are not official SSC/IBPS/RRB papers.
