Friday, October 9 — Day 29

The first number they both reach.

The clock

Same block. 9:30 start, the printed sheet at 10:30 with the filled side down, exam 12:30–1:00, phones off until 1:30. The sheet is on the desk. Put it away before the exam.

The idea

LCM means least common multiple. List the multiples of each number. The answer is the first number that shows up in both lists.

4 and 6.

4, 8, 12, 16, …

6, 12, 18, …

They meet at 12.

5 and 7.

They meet at 35. Neither is a multiple of the other, so the meeting point is their product.

If one number is already a multiple of the other, that number is the LCM. 5 and 15 meet at 15.

GCF is the largest number that divides both. It goes down. LCM goes up. The exam says LCM on every one of these.

Help

• LCM