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 = 80*t* km

The taxi travelled = 60*t* km

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

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

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