sugu86 wrote:
If k^3 is divisible by 240 what is the least possible value of integer K?
A. 12
B. 30
C. 60
D. 90
E. 120
Since k^3/240 = integer, we can say that the product of 240 and some integer n is equal to a perfect cube. In other words, 240n = k^3.
We must remember that all perfect cubes break down to unique prime factors, each of which has an exponent that is a multiple of 3. So let’s break down 240 into primes to help determine what extra prime factors we need to make 240n a perfect cube.
240 = 24 x 10 = 8 x 3 x 2 x 5 = 2 x 2 x 2 x 3 x 2 x 5 = 2^4 x 3^1 x 5^1
In order to make 240n a perfect cube, we need two more 2s, two more 3s and two more 5s. Thus, the smallest perfect cube that is a multiple of 240 is 2^6 x 3^3 x 5^3.
To determine the least possible value of k, we can take the cube root of 2^6 x 3^3 x 5^3 and we have:
2^2 x 3 x 5 = 4 x 3 x 5 = 60
Thus, the minimum value of k is 60.
Answer: C
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