Number System
-  How many 3-digit numbers, in all, are divisible by 6 ?
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                        View Hint View Answer Discuss in Forum First 3–digit number divisible by 6 = 102 
 Last such 3-digit number =996
 ∴ 996 = 102 + (n –1) 6
 ⇒ (n – 1)6 = 996 – 102 = 894Correct Option: BFirst 3–digit number divisible by 6 = 102 
 Last such 3-digit number =996
 ∴ 996 = 102 + (n –1) 6
 ⇒ (n – 1)6 = 996 – 102 = 894⇒ n – 1 = 894 = 149 6 
 ⇒ n = 150
 Hence , required answer is 150.
-  The total number of integers between 100 and 200, which are divisible by both 9 and 6, is :
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                        View Hint View Answer Discuss in Forum A number is divisible by 9 and 6 both, if it is divisible by LCM of 9 and 6 i.e., 18. Correct Option: BA number is divisible by 9 and 6 both, if it is divisible by LCM of 9 and 6 i.e., 18. Hence, the numbers are 108, 126, 144, 162, 180, 198. 
 Thus , the total number of integers between 100 and 200 are 6.
-  The least number, which must be added to 6709 to make it exactly divisible by 9, is
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                        View Hint View Answer Discuss in Forum A number is divisible by 9 if the sum of its digits is divisible by 9. 
 Here, 6 + 7 + 0 + 9 = 22Correct Option: AA number is divisible by 9 if the sum of its digits is divisible by 9. 
 Here, 6 + 7 + 0 + 9 = 22
 Now, 22 + 5 = 27, which is divisible by 9. Hence 5 must be added to 6709.
-  If 5432*7 is divisible by 9, then the digit in place of * is :
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                        View Hint View Answer Discuss in Forum A number is divisible by 9, if sum of its digits is divisible by 9. 
 Let the number be p.
 ⇒ 5 + 4 + 3 + 2 + p + 7Correct Option: CA number is divisible by 9, if sum of its digits is divisible by 9. 
 Let the number be p.
 ⇒ 5 + 4 + 3 + 2 + p + 7
 ⇒ 21 + p
 ⇒ 21 + 6 = 27, which is divisible by 9.
 ∴ p = 6
 Therefore , the digit in place of * is 6 .
-  (49)15 – 1 is exactly divisible by :
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                        View Hint View Answer Discuss in Forum As we know that , 
 xn – an is exactly divisible by (x – a) if n is odd.Correct Option: DAs we know that , 
 xn – an is exactly divisible by (x – a) if n is odd.
 ∴ (49)15 – (1 )15 is exactly divisible by 49 – 1 = 48, that is a multiple of 8.
 Hence required answer is 8.
 
	