40 pages: 1. Common multiple. Least common multiple. 2. A smaller number. A bigger number. 3. Multiples of two numbers. 4. multiples, etc. Multiples, etc. 5. A countless 2. ×, √, ×, √. Third, AC, AB. Forget those four questions. 5. Find the greatest common factor of 15 and 18, which is equal to 3, and then use 18÷3. Then write: the least common multiple is 15×6=90. Answer: There are at least 90 people involved in planting trees.