To convert units, we use conversion factors. For example, we are going to write 5 000 s in hours. Multiplying an amount by a conversion factor is like multiplying it by 1; the amount does not change, only the units do. 5.1. Converting units of time In the SI, time is measured in seconds (s). If it is a large amount, it is usually measured in minutes, hours, days or years. If it is small , it is measured in tenths, hundredths or thousandths of a second. 5. Converting units 46 WORK WITH THE IMAGE. Are the contents of the packaging in the images expressed in the same unit? What are the advantages and disadvantages of each of these types of packaging? 47 If you were organising a party for 20 people, which type of packaging would you choose? Why? A conversion factor is a fraction that has equal amounts in the numerator and denominator, but expressed in dif ferent units. × 10 × 10 × 10 × 60 × 60 × 24 : 24 : 60 : 60 : 10 : 10 : 10 d (day) h (hour) min (minute) s (second) ds (tenth of a second) cs (hundredth of a second) ms (thousandth of a second) 2. Write the conversion factor. a) Beside the amount, put a dot (multiplication sign) and the fraction bar. b) Write the initial unit and the final unit in the correct places to simplify the initial unit. c) Write the equivalence between the units. a) 5 000 s × b) 5 000 s × h s c) 5 000 1 3 600 s h s × 1. Find the equivalence between the initial unit and the final unit × 60 × 60 h (hour) min (minute) s (second) 1 h = 60 × 60 = 3 600 s 3. Simplify the units. Calculate and write the final result in the new unit. 5 000 5 000 1 3 600 s s h s = ⋅ =1.39 h Conversion factor To convert minutes into hours, we use the corresponding conversion factor, taking into account that 1 h = 60 min . 75 1 60 1 25 min min . ⋅ = h h Remember that 1.25 hours is equal to one and a quarter hours, and not one hour and 25 minutes. 1.25 h 1 h 0.25 × 60 = 15 min 1 h 15 min CHALLENGE Conversion factor 26
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