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The problem: If k is an integer and \((0.0025)( 0.025)( 0.00025) × 10k\) is an integer, what is the least possible value of k?
The solution (from the Official 2016 Guide to GMAT): Let \(N = (0.0025)( 0.025)( 0.00025) × 10^k\) ...etc etc Why \(10*k\) has become \(10^k\) in the solution???
Right to knowledge, this is the full explanation: Let \(N = (0.0025)( 0.025)( 0.00025) ×10^k\). Rewriting each of the decimals as an integer times a power of 10 gives \(N = (25 × 10 ^{− 4})( 25 × 10^{ − 3})( 25 × 10^{ − 5}) × 10^k = (25^3) × 10^{k − 12}\). Since the units digit of \((25^3)\) is 5, it follows that if k = 11, then the tenths digit of N would be 5, and thus N would not be an integer; and if k = 12, then N would be \((25^ 3) × 10^0 = (25^ 3)\), which is an integer. Therefore, the least value of k such that N is an integer is 12.
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The problem: If k is an integer and \((0.0025)( 0.025)( 0.00025) × 10k\) is an integer, what is the least possible value of k?
The solution (from the Official 2016 Guide to GMAT): Let \(N = (0.0025)( 0.025)( 0.00025) × 10^k\) ...etc etc Why \(10*k\) has become \(10^k\) in the solution???
Right to knowledge, this is the full explanation: Let \(N = (0.0025)( 0.025)( 0.00025) ×10^k\). Rewriting each of the decimals as an integer times a power of 10 gives \(N = (25 × 10 ^{− 4})( 25 × 10^{ − 3})( 25 × 10^{ − 5}) × 10^k = (25^3) × 10^{k − 12}\). Since the units digit of \((25^3)\) is 5, it follows that if k = 11, then the tenths digit of N would be 5, and thus N would not be an integer; and if k = 12, then N would be \((25^ 3) × 10^0 = (25^ 3)\), which is an integer. Therefore, the least value of k such that N is an integer is 12.
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Hi, shifting your Query to general maths..
if the Q is "If k is an integer and \((0.0025)( 0.025)( 0.00025) × 10^k\) is an integer, what is the least possible value of k?" and that seems is the case from other discussions done on this site, then the answer is ofcourse what is explained as it is..
but say it is 10*k.., then the answer will change.. you will have to recheck it..
The problem: If k is an integer and \((0.0025)( 0.025)( 0.00025) × 10k\) is an integer, what is the least possible value of k?
The solution (from the Official 2016 Guide to GMAT): Let \(N = (0.0025)( 0.025)( 0.00025) × 10^k\) ...etc etc Why \(10*k\) has become \(10^k\) in the solution???
Right to knowledge, this is the full explanation: Let \(N = (0.0025)( 0.025)( 0.00025) ×10^k\). Rewriting each of the decimals as an integer times a power of 10 gives \(N = (25 × 10 ^{− 4})( 25 × 10^{ − 3})( 25 × 10^{ − 5}) × 10^k = (25^3) × 10^{k − 12}\). Since the units digit of \((25^3)\) is 5, it follows that if k = 11, then the tenths digit of N would be 5, and thus N would not be an integer; and if k = 12, then N would be \((25^ 3) × 10^0 = (25^ 3)\), which is an integer. Therefore, the least value of k such that N is an integer is 12.
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.