Quantitative Aptitude :: Problems Based on Number Formulas

Problems Based on Number Questions and Answers

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Problems Based on Number


Problems on numbers can be solved by analysing the given statements and by framing the respective linear or quadratic eqution and solving for the unknowns. Solved Examples

Type 1 Words Problems
					   
	Example 1: The sum of an integer and its reciprocal is 17/4. Find the number.
	Solution.  Let the number be x. Then.
	                 x + 1/x = 17/4 => (x2 + 1)/x = 17/4
			=>                 4x2 - 17x + 4 = 0
			=>                 4x2 - 16x - x + 4 = 0
			=>           4x(x - 4) - 1(x - 4) = 0 => (4x - 1)(x - 4) = 0
			=>                                         x = 4 or 1/4
			Hence, the number is 4.      (1/4 is not an integer)
			
	Example 2: If the sum of two numbers is 52 and their product is 672, then find the absolute 
	           difference between the numbers.
	Solution. Let the numbers be x and y. Then, x + y = 52 and xy = 672
	             x - y = √(x + y)2 - 4xy  =  √(52)2 - 4 x 672 = √2704 - 2688 = √16 = 4
		.: Required difference = 4 
		
    Example 3: A number consists of two digits. The sum of the digits is 6. If 18 is subtracted
            	from the number, its digit are interchanged. Find the number.
	Solution. Let the ten's digit be x.
	Then, Unit's digit = (6 - x)
	      Number = 10x + (6 - x) = 9x + 6
	Number obtained by reversing the digits
	         = 10(6 - x) + x = 60 - 9x 
		.: 9x + 6 - 18 = 60 - 9x
		=>         18x = 72 
		=>           x = 4 
		Hence, the required number is 42.
		
Type 2 Data Sufficiency
Directions (Examples 4 to 5) : In each of the following questions, a question followed by two statements numbered I and II are given. You have to read both the statements and then Give answer (1). If the data given in statement A alone are sufficient to answer the question whereas the data given in statement B alone are not sufficient to answer the question (2). If the data given in statement B alone are sufficient to answer the question whereas the data given in statement A alone are not sufficient to answer the question (3). If the data in either statement A alone or in statement B alone are sufficient to answer the question (4). If the data in both the statements A and B are not sufficient to answer the question (5). If the data given in both the statements A and B are necessary to answer the question Example 4 : What is the two-digit number? A. The difference between the two digits is 8 B. The sum of the digits is equal to the difference between the two digits. Solution. (5) Let the ten's and unit's digit be x and y respectively. Then, from A, x + y = 8 and B, x - y = 8 Upon solving, we get x = 8 and y = 0 .: Required number = 80 Thus, both A and B are needed to get the answer. Example 5 : What is the two-digit number? A. Sum of the two digits is 7. B. The digit in the ten's place is bigger than the unit's place by 1. Solution. (5) Let the ten's and unit's digit be x and y respectively. Then, from A, x + y = 7 and from B, x - y = 1 Upon solving, we get x = 4 and y = 3 .: Required number = 43 Thus, both A and B are needed to get the answer.