Sarin’s father crossing the Causeway part 6(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 UPQ84

Sarin’s father travelled within JB town on bicycle. He planned to cycle from City Square to Jesco. If he were to cycle at 10 km/h, he would reach Jesco at 7.45 p.m. If he were to cycle at 12 km/h, he would reach Jesco at 7.15 p.m. What was the distance between the two places?

Solution:

                        Distance = speed × time

                        If he travelled at 10km/h, he needed extra 30minutes or ½ hour

                        Distance cover by that extra 30minutes = 10 × ½ = 5km

                        If he travelled at speed of 12km/h, 2km extra distance will cover within an hour

                        Or, 1 km extra per ½ hr

                       He needed 5 of ½ hour or total 5 ÷ 2 = 2.5hr to cover the distance with speed of 12km/h.

                        Draw a model on distance and speeds,

  

                        Distance between the two places =12 × 2.5 = 30km

                        Alternative solution:

                                    Distance = speed × time

                                    Distance is fixed, with different speed, time taken will be different.

                                    In these case, the time different is 30minutes or ½ hour

                                    Also faster in speed, shorter the time taken,

                                    So, if you need t hour for travel at 12km/h, travel at 10km/h will need

                                    (t + ½) hours to cover the same distance.

                                                Distance = 12 × t = 10 × (t + ½)

                                                12t = 10t + 5

                                                t = 5/2 hours = 2.5 hours

                                                Distance between the two places = 12 × 5/2 = 30km

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