# Sarin’s father visits his friend in JB town (Math Question)

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Sarin’s father has a friend that stays in JB town. He is one of the long lost friend of his father and get back into contact after his friend found out his father’s telephone number via checking out from the Singapore residential telephone book. Sarin’s father decides to visit his friend that stays in JB town after receiving the first emotional and excited call from his friend.

JB is the short form of Johor Bahru that Singaporeans and Malaysians use to address this southern most city of Malaysia. It is the capital of Johor state in southern peninsular Malaysia and just across a kilo meter length causeway from Singapore. Singaporeans can go to JB by driving or taking public buses across the causeway (strait bridge) and it is one of the usual past-time places for Singaporeans to visit during weekends or short holidays. Singaporeans stop by JB for budget shopping, cheap local foods and daily items.

Like to know more about how to travel to JB from Singapore as well as the places to visit you can go to  http://wikitravel.org/en/Johor_Bahru

Upper primary school mathematics question UPQ4

Sarin’s father is driving from Simei estate in Singapore to visit his friend live in JB town. If he travels at an average speed of 40km/h, he will reach JB town at 12 noon. But if he travels at 50km/h, he will reach JB town at 10am. What should his average speed be if he wants to reach JB town at 11am?

Solution:

If travel at 40km/h, will need extra 2 hours to complete the distance

The distance travelled in the 2 hours = 40 × 2 = 80km

Compared the speed of 50km/h and 40km/h

The extra distance covered by 50km/h in 1 hour = 50 – 40 = 10km

The number of hours need to cover the completed distance when travel at 50 km/h = 80 ÷ 10 = 8 h

The total distance travelled = 50 × 8 = 400km

To reach JB town at 11a.m., travel duration = 8 + 1 = 9 h

The speed for travel so to reach JB town at 11 a.m. = 400 ÷ 9 = 44.4 km/h

Alternative Solution(1):

The multiples in distance based on 40km/h

40, 80, 120, 160, 200

The multiples in distance based on 50 km/h

50, 100, 150, 200

So, at 200km, the travel time difference is 1 h

Since the actual diference in time is 2 h, the total distance from Simei estate to JB town = 2 × 200 = 400 km

The time taken to travel to JB town with the speed of 40km/h is 10 h

To reach JB town at 11.00 a.m., the travel time = 9 h

The speed need for travel 9 h = 400 ÷ 9 = 44.4 km/h

Alternative Solution(2):

The ratio of the speed = 40 : 50 = 4 : 5

The time difference to reach JB town = 2 h

1 unit = 2h

The time taken to travel to JB town with the speed of 40 km/h = 2 × 10 = 10 h

The distance from Simei estate to JB town = 10 × 40 = 400 km/h

To reach JB town at 11 am., the speed = 400 ÷ 9 = 44.4 km/h

Alternative Solution(3):

Using Algebra or Equation,

Set D be the distance between Simei estate to JB town,

The diference in time to reach JB town is 2 h

D/40 – D/50 = 2

50D/2000 – 40D/2000 = 2

D/200 = 2

D = 400 km

To reach JB town at 11 am., the speed = 400 ÷ 9 = 44.4 km/h