Other Bases of Counting: Seven and Sixty
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There are seven days in a week. Suppose that a baby is 2 weeks and 5 days old. This means that it is 2 lots of 7 days and 5 days old, 19 days altogether.
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Example 1

Find the total of 1 week 5 days, 6 days and 3 weeks 4 days. Give the answer a) in weeksand days, b) in days. Solution a) wk d 1 5 6 3 4 ====== 6 1 Method in days column: 5 + 6 + 4 = 15 days = 2 x 7 days + 1 day = 2 weeks + 1 day write down 1 day and carry 2 weeks answer: 6 weeks and 1 day b) 6 wk 1 d = 6 x 7 days + 1 day = 42 days + 1 day = 43 days
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Example 2

Today is Wednesday. What day of the week will it be in 160 days time? Change 160 days to weeks and days. 160 d = 160 / 7 wk = 22 wk 6 d After 22 weeks it will be Wednesday again. Count a further 6 days on from Wednesday: Thursday, Friday, Saturday, Sunday, Monday, Tuesday. It will be Tuesday in 160 days time. There are 60 seconds in a minute and 60 minutesin an hour.
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Example 3

Find the number of seconds in 3 min 49 s. Number of seconds in 3 min = 3 x 60 s = 180 s Number of seconds in 3 min 49 s = 180 s + 49 s = 229 s
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Example 4

Add the following times together. Give the answers in hours and minutes. 3 h 40 min, 2 h 25 min, 28 min, 1 h 35 min h min Method in minutes column: 3 40 40 + 25 + 28 + 35 = 128 min 2 25 = 2 x 60 min + 8 min 28 = 2 h 8 min 1 35 write down 8 min and carry 2 h 8 8 answer: 8 h 8 min
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