--- title: "Time zones" subtitle: "Area, volume, circles and Pythagoras · Time zones · Lesson 18" --- # Time zones **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** You call your cousin in London after school and wake her up at 5 am. A flight from Sydney lands in Los Angeles before it took off. Time zones explain both. :::teacher-note **In one sentence:** Students move one city's time and watch the others follow, convert between time zones using UTC offsets, and plan flights and a call across zones (AC9M8M04, nodes 1 and 2). **Students should be able to say:** I can change a time from one time zone to another using UTC offsets. I can tell when the day changes. I can work out when a flight lands, in local time. **Width:** the unmarked parts are the floor every student does (predict, run, investigate and make). Typical adds the modify practice; wider adds the real-world contexts. They add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Predict Is London ahead of Sydney or behind? :::keep-together **It is 9:00 am Monday in Sydney (UTC+11). What time is it in London (UTC+1)?** ☐ 10:00 am Monday ☐ 7:00 pm Sunday ☐ 11:00 pm Sunday ☐ 7:00 pm Monday My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** 11:00 pm Sunday. London is 10 hours behind Sydney: 9:00 am − 10 hours goes back past midnight to 11:00 pm the day before. ::: ## Run Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Ahead and behind :::keep-together ### Perth Here is the routine. 1. $+11 - (+1) = 10$ — The difference between the offsets: 10 hours. 2. $\text{London's offset is smaller}$ — So London is behind Sydney. 3. $09{:}00 - 10\ \text{h} = 23{:}00\ \text{the day before}$ — Take it away, crossing midnight back to Sunday. Now find Perth's time. **It is 14:00 in Sydney (UTC+11). What hour is it in Perth (UTC+8), in 24-hour time?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 11 Perth is 11 − 8 = 3 hours behind: 14:00 − 3 = 11:00. ::: :::keep-together ### Find the mistake **Kim finds the time in London. Click the line where her working goes wrong.** ``` 1 It is 9:00 am Monday in Sydney (UTC+11). Kim wants the time in London (UTC+1). 2 The zones are 10 hours apart, so she adds 10 hours. 3 London time is 7:00 pm Monday. ``` Line: {{field-15}} Why is it wrong? {{lines-2}} ::: :::teacher-note **Answer:** line 2 Line 2: London's offset (+1) is smaller than Sydney's (+11), so London is behind: take 10 hours away. 9:00 am Monday becomes 11:00 pm Sunday. ::: :::keep-together ### 24-hour time **Why do flight times use 24-hour time?** ☐ It is shorter to write ☐ Airports are open 24 hours ☐ 21:30 cannot be mixed up with 9:30 in the morning ☐ It changes the time zone ::: :::teacher-note **Answer:** 21:30 cannot be mixed up with 9:30 in the morning With 12-hour time, a missing am or pm causes 12-hour mistakes. ::: :::typical ## Going the other way, and flights **London to Sydney.** **A flight.** **Two offices.** **Plan a call.** Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} ::: ## Time zones :::keep-together ### Sydney to Perth **It is 10:00 in Sydney (UTC+11). What hour is it in Perth (UTC+8), in 24-hour time?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 7 Perth is 3 hours behind: 10:00 − 3 = 07:00. ::: :::keep-together ### A trip's length **A train leaves at 08:45 and arrives at 17:20 the same day (one time zone). How many minutes is the trip?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 515 08:45 to 17:00 is 8 h 15 min; plus 20 min is 8 h 35 min = 515 minutes. ::: :::keep-together ### 12-hour time **What is 21:45 in 12-hour time?** ☐ 11:45 pm ☐ 10:45 pm ☐ 9:45 pm ☐ 9:45 am ::: :::teacher-note **Answer:** 9:45 pm 21 − 12 = 9: 9:45 pm. ::: :::keep-together ### Past midnight **It is 23:00 on Sunday in Perth (UTC+8). What hour is it in Sydney (UTC+11), in 24-hour time? (It is Monday there.)** Answer: {{field-15}} ::: :::teacher-note **Answer:** 2 23:00 + 3 hours = 02:00 on Monday. ::: :::keep-together ### A flight's length **A flight leaves Perth at 06:00 Perth time and lands in Sydney at 13:00 Sydney time. How many hours is the flight?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 4 06:00 in Perth is 09:00 in Sydney; 09:00 to 13:00 is 4 hours. ::: ## Make: plan an arrival Then write both times for your flight, in 24-hour time with the day, as you would on a ticket. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} ## Exit ticket :::keep-together **It is 18:30 Tuesday in Sydney (UTC+11). What time and day is it in Los Angeles (UTC−7)?** {{lines-3}} ::: :::teacher-note **Answer:** Los Angeles is 18 hours behind: 00:30 Tuesday. :::