Multiples

Part of the Factors & Fractions section of Coddy's Pre-Algebra journey. Lesson 4 of 58.

The multiples of a number are what you get when you multiply it by 1, 2, 3 and so on. The multiples of 7 are 7, 14, 21, 28, and the list never ends: you are counting by sevens. Multiples and factors are two views of one fact: 7 is a factor of 21, and 21 is a multiple of 7.

Multiples count things that repeat. A tram leaves at 9:00, and after that one leaves every 15 minutes. The next leaves at 9:15, which is 1 × 15 minutes after 9:00, and the one after that at 9:30, 2 × 15 minutes after. So the 3rd tram after the 9:00 one leaves 3 × 15 minutes after 9:00. Use t for time: t = 3 × 15, then t = 45. It leaves at 9:45.

Watch the count. The 9:00 tram is zero gaps after 9:00, so the 3rd tram after it is 3 gaps of 15 minutes later, not 4. Counting gaps rather than trams keeps you from being one step off.

Challenge

The first bus leaves the station at 8:00. After it, a bus leaves every 12 minutes, so the next one leaves at 8:12. How many minutes t after 8:00 does the 5th bus after the 8:00 bus leave? Write t equal to the calculation, work it out on the next line, then press Check.