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8–7Measures of TimeEXAMPLE Add Units of TimeMAIN IDEA• Add and subtractmeasures of time.KEY CONCEPTUnits of Time1 second (s)time needed to say 1,0011 minute (min) = 60secondstime for 2 average TVcommercials1 hour (h) = 60 minutestime for 2 weekly TVsitcomsFind the sum of 3 h 15 min 52 s and 1 h 42 min 11 s.Estimate 3 h 15 min 52 s + 1 h 42 min ≈3 h 15 min 52 sh + h or 5 h._____________+ 1 h 42 min 11 sh min s4 h 57 min (1 min 3 s)4 h min 3 sAdd seconds fi rst, then minutes,and fi nally hours.63 seconds is greater than60 seconds or minute.Rename 63 seconds.Add minutes.Check for Reasonableness 4 h 58 min 3 s ≈ 5 h ✔EXAMPLEMARATHONS The table shows the times of the winnersof the men’s and women’s races at the 2007 BostonMarathon. How much faster was Cheruiyot’s time thanGrigoyeva’s time?Race Runner TimeMen’s Cheruiyot 2 h 14 min 13 sWomen’s Grigoyeva 2 h 29 min 18 sEstimate 2 h 29 min 18 s - 2 h 14 min 13 s ≈2 h 29 min 18 s_________- 2 h 14 min 13 sminmin - min or minsSubtract the seconds fi rst,then minutes, and fi nallythe hours.Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.210 Math Connects, Course 1Cheruiyot’s time was minutes seconds faster thanGrigoyeva’s time. 15 min 5 s ≈ 15 min ✔