This blog is managed by Song Hock Chye, author of Improve Your Thinking Skills in Maths (P1-P3 series), which is published and distributed by EPH.

Thursday, April 02, 2009

Rosyth Sch 2006 PSLE Math Prelim Q33

The graph below shows the distance traveled by Mark in 4 hours. What was Mark’s average speed?


Solution

Speed = Distance divided by time
Speed = 260 km divided by 4 h = 65 km/h (Answer)

5 comments:

Confuse said...

Please assist. Thanks

Question:

A wave of the water current is flowing at a speed of 8 km/h towards Point X from Point Y which was 877 km apart.
At 8 am, Johnny rode off with his boat at a speed of 50 km/h towards Y from Point X for 30 mins and then stopped to have a rest for 45 mins before continuing his remaining journey at the same speed. At 9.15 am, Peter set off with his boat at a speed of 120 km/h from Point Y to Point X and both of them travelled for a distance and finally met at Point Z. How long did Johnny take to travel after passing Peter at Point Z? Express your answer in hrs. [ 5 Marks ]

Ans: 6 1/4 hrs

Deal with Logic said...

Question :

A wave of the water current was flowing at a speed of 8 km/h towards Point X from Point Y which was 865 km apart.
At 8 am, Johnny rode off with his boat at a speed of 50 km/h towards Y from Point X for 30 mins and then stopped to have a rest for 45 mins before continuing his remaining journey at the same speed. At 9.15 am, Peter set off with his boat at a speed of 120 km/h from Point Y to Point X and both of them travelled for a distance and finally met at Point Z. How long did Johnny take to travel after passing Peter at Point Z? Express your answer in hrs. [ 5 Marks ]

Solution: Logic reasoningSpeed of current from Y to X
= 8 km/h

Speed of Johnny from X to Y
= 50 - 8
= 42 km/h

Note: Current was flowing in the opposite direction. When Johnny was roding forward from X to Y, the current will push his boat by
8 km backwards instead of forwards.

Distance travelled by Johnny after 30 mins
= 42 km/h * 1/2 hr
= 21 km

*Distance travelled by the boat after 45 mins
= 8 km/h * 3/4 hr
= 6km

*Note: As the Johnny's boat stopped and have a rest for 45 mins, the wave of the water current is pushing the boat backwards.

Total distance travelled by the boat
= 21 - 6
= 15 km

Remaining distance
= 865 - 15
= 850 km

*Speed of Peter and current
= 120 + 8
= 128 km/h

*Note: Peter was roding the boat from Y to X at the same direction with the wave. He rode 120 km and the wave will move the boat 8 km forward in 1 hr.


Sum of speed by Johnny and Peter
= 42 + 128
= 170 km/h

Time taken to meet after 0915 hrs
= 850 / 170
= 5 hr

Time taken for Johnny
= 1/2 hr + 3/4 hr + 5 hr
= 6 1/4 hr


Hope that i am not wrong. This question tests the students' understanding of logic reasoning although this question is rare.

Anonymous said...

So simple.... don't understand why people will ask this type of simple logicial problems!

Anonymous said...

Question should be - How long had Johnny travelled before he met Peter at Point Z?

fahrenheit_rox_97 said...

I thought Peter was traveling the direction opposite the waves? The wave is traveling from X to Y but Peter is traveling from Y to X.