BECE Mathematics 2014 Paper

Concept:The smallest number divisible by both 16 and 20 is their Least Common Multiple (LCM).Explanation:Write each number as a product of prime factors.$16 = 2 \times 2 \times 2 \times 2 = 2^4$$20 = 2 \times 2 \times 5 = 2^2 \times 5$For the LCM, take every prime factor with the highest power that appears in either number.The highest power of 2 is $2^4$ and the highest power of 5 is $5^1$.Therefore, LCM $= 2^4 \times 5 = 16 \times 5 = 80$.Thus, 80 is the smallest number divisible by both 16 and 20.Answer:B. 80