MATHEMATICS Time – Telling the Time

Lesson Objectives The aim of this powerpoint is to help you… Learn how to tell the time Learn how to change between 12 hour and 24 hour clock times

Digital or Analogue Clock Faces Digital clock faces give you 4-digit times quoting 12 hour or 24 hour clock. Analogue clock faces show the hours (1 to 12) around the outside and have two hands (or pointers). The short hand points to the hour-value. The minute hand points to the minute-value.

Analogue Clocks Let’s take a look at times on analogue clocks… Here is a clock face. The hours are labelled 1-12 around the outside. These are also the marks for each set of 5 minutes. When quoting time… we look at which hour the shorter hand is pointing towards – if it is between two numbers, choose the smaller value. we work out how many minutes the longer hand is pointing towards – remember go up in 5s

Examples The hour hand is between 5 and 6 – the smaller is 5! The minute hand is at 2 lots of 5 = 10 The time is 5: The hour hand is between 11 and 12 – the smaller is 11! The minute hand is just after 9 lots of 5 (=45), so probably 46 The time is 11:46

Telling the Time If you are not confident in telling the time, then you need to work through the MyMaths lesson called Telling the Time 1 It can be found at this URL:

Telling the Time There are two ways of telling the time: Using a 12 hour clock system and the letters a.m. (ante-meriden – before midday) for morning times and p.m. (post-meriden – after midday) for afternoon times; Using a 24 hour clock system – 4 digits (2 for hours and 2 for minutes) and NO a.m. or p.m., as used in timetables.

Changing 12 hour to 24 hour clock times For 12am-12:59am times, drop the a.m. and change the 12 (hours) to 00 For 1am-11:59am times, drop the a.m. and write any hours before 10 with a zero in front. For 12pm-12:59pm times, drop the p.m. For 1pm-11:59pm times, drop the p.m. and add 12 on to the hours.

Quick Practice Change these 12 hour clock times to 24 hour ones: 1) 4:26am = 6) 4:26pm = 2) 7:39am = 7) 12:43pm = 3) 5:28pm = 8) 9:18am = 4) 10:12am = 9) 12:51am = 5) 11:07pm = 10) 3.29pm = Work out your answers before clicking on to the next slide.

Quick Practice - Answers 1) 4:26am = Drop am, put 0 in front of 4 … 2) 7:39am = Drop am, put 0 in front of 7 … 3) 5:28pm = Drop pm, add 12 on to 5 … 4) 10:12am = Drop am … 5) 11:07pm = Drop pm, add 12 on to 11… 6) 4:26pm = Drop pm, add 12 on to 4 … 7) 12:43pm = Drop pm … 8) 9:18am = Drop am, put 0 in front of 9 … 9) 12:51am = Drop am, change 12 to 00 … 10) 3.29pm = Drop pm, add 12 on to 3 …

Changing 24 hour to 12 hour clock times Times beginning with 00.. should be written as 12.. with an a.m. at the end For times beginning (inclusive) drop any unnecessary zeros at the front of the hours and write a.m. at the end Times beginning with 12.. should be written with a p.m. at the end For times beginning 13.. – 23.. (inclusive) subtract 12 from the hours and write p.m. at the end

Quick Practice Change these 24 hour clock times to 12 hour ones: 1) 0348 = 6) 0008 = 2) 1205 = 7) 0817 = 3) 2111 = 8) 1356 = 4) 1724 = 9) 1022 = 5) 1130 = 10) 1805 = Work out your answers before clicking on to the next slide.

Quick Practice - Answers 1) 0348 = Drop the front 0, add a.m. … 2) 1205 = Add p.m. … 3) 2111 = Subtract 12 from 21, add p.m. … 4) 1724 = Subtract 12 from 17, add p.m. … 5) 1130 = Add a.m.… 6) 0008 = Change 00 to 12, add a.m. … 7) 0817 = Drop the front 0, add a.m. … 8) 1356 = Subtract 12 from 13, add p.m. … 9) 1022 = Add a.m. … 10) 1805 = Subtract 12 from 18, add p.m. … 3:48am 12:05pm 9:11pm 5:24pm 11:30am 12:08am 8:17am 1:56pm 10:21am 6:05pm

What next? Print out the notes called Time1. Read through them and make sure you answer any questions. Save and complete the worksheet: Time-S1.xlsx Now move on to the Time2 powerpoint