19. State the smallest integer that is divisible by both 20 and 45.
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The smallest integer that is divisible by both 20 and 45 is actually the least common multiple (LCM) of the two numbers. To find the LCM, we can use their prime factorizations: 20 = 2^2 × 5 and 45 = 3^2 × 5. The LCM is found by taking the highest power of each prime: LCM = 2^2 × 3^2 × 5 = 4 × 9 × 5 = 180. Thus, the answer is 180. Now, if you're ever in a pinch trying to find the LCM, remember you can also use the relationship between the greatest common divisor (GCD) and the LCM: LCM(a, b) = (a × b) / GCD(a, b). It’s a great way to simplify calculations, especially for larger numbers! Also, if you’re interested in diving deeper into number theory, check out books like "Elementary Number Theory" by David M. Burton or "An Introduction to the Theory of Numbers" by G.H. Hardy and E.M. Wright. They provide great insights and fun problems to enhance your understanding of integers and their properties!