23X5
The prime factorization of 40 is 2x2x2x5 or 23x5.
The prime factorization of 32 is 2x2x2x2x2 or 25. The prime factorization of 40 is 2x2x2x5 or 23x5. For a number to be a multiple of a given number the multiple must have the entire prime factorization of that number in is. So a multiple of 32 must contain 2x2x2x2x2 or 25 . Likewise a multiple of 40 must contain 2x2x2x5 or 23x5. The least number that this could possible happen with must have 5 factors of 2 and one factor of 5 (the highest exponent on each individual prime factor). Thus the LCM is 2x2x2x2x2x5 or 25x5 Which is 160.
Boy, I wish this website could notate exponents properly. If that's 24 x 3 x 5 and 23 x 52, the GCF is indeed 23 x 5. Good job. In other words, the GCF of 240 and 200 is 40.
If a number is a perfect square, then its prime factors can be split into two identical groups: if a perfect cube, three groups; if a perfect fifth power, five groups. The best way to attain this sort of 'symmetry' is to only use one prime factor. Since we are looking for small (ish) solutions, we'll use 2. It only remains to decide how many 2's to multiply together. The number needs to be divisible by 2, 3 and 5. We are looking for the lowest common denominator of 2, 3 and 5, which is 30. 22x3x5 = 230 = 1073741824 = (22x3)5 = (22x5)3 = (23x5)2 The next smallest solution is given by 330 = 205891132094649, which is just a little bit bigger than 2 x 1014. So the question is correct in assuming that only one answer exists.