Sarin’s father crossing the Causeway part 7(Math Question)

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Read posting on Sarin’s father visits his friend in JB town to know about JB town as well as reading posting on Sarin’s father crossing the Causeway to know about the Johor-Singapore Causeway.

Read also posting on Sarin learns rate of change in school (Math Concept) to learn about concept of speed and relative speed. 

Upper primary school mathematics question UPQ112

Simei and JB Town were 361 km apart. At 06 00, Sarin’s father started travelling from Simei to JB Town at a constant speed of 80 km/h. 45 minutes later, a taxi left JB Town and travelled towards Simei at a constant speed of 60 km/h. At what time did Sarin’s father and the taxi pass each other?

Solution:

                        The taxi only start after 45 minutes later,

                        Sarin’s father had covered 80 × 45 /60 = 60km

                        Distance between Sarin’s father and the taxi is 361 – 60 = 301km before taxi left JB Town

                        Using relative speed concept, the relative speed among them = 80 + 60 = 140km/h

                        Time taken to travel the distance of 301km = 301 ÷ 140 = 2.15 hrs = 2 h 9mins

                        Time that they pass each other = 06 00 + 00 45 + 02 09 = 08 54

Alternative solution:     

                        Draw a distance model when taxi left JB Town,

                        If both of them pass each other after t hours,

                        Sarin’s father travelled = 80t km

                        The taxi travelled = 60t km

                        The distance cover = 301 = 80t + 60t =140t

                        The time taken to travel 301km = 301 ÷ 140 = 2h 9mins      

                        Time that they pass each other = 06 00 + 00 45 + 02 09 = 08 54

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