Distance Speed and Time: Mrs Jones takes 2 min to walk to her car...

[Mamabear]

Hi, my son's maths assignment is proving to be a challenge and I need help understanding something please. I apologise if this will be a long post!

1) Mrs Jones takes 2 min to walk to her car, 30 sec to get out of the gate, drives 1 km at 40 kmh and then takes 2 minutes to find a park and another minute to walk from the parking space.

Our answer is 5.5 minutes plus 1.5 minutes for driving the 1 km which gives us 7 minutes in total. We added up the time it took doing everything and then went 60 divided by 40 to give us the 1.5 minutes to drive the 1 km. Using Time = Distance/Speed means that we have to divide 1km by 40?

2) Mrs Smith walks to the shops and only has to walk 650 metres. How fast would she have to walk to beat Mrs Jones to the shops?

We have no idea how to work this out given just one bit of information. We think it takes Mrs Jones 7 minutes so I am thinking we need Mrs Smith to walk the 650 metre distance in less than 7 minutes but how do we work this out showing the working?

3) A student thinks she can ride faster. She rides at 20 kmh at the same distance of Mrs Smith (650 metres). Will she be the fastest?

Now here we have used the Time = Distance/Speed and get 32.5 but logically speaking if she can ride 20km in one hour, she can ride 650 metres in 1 minutes and 57 seconds. We don't know which is the correct answer or working out.

I am so confused as to if the answer is 1.57 minutes or 32.5????

I hope someone can help me understand this as I am pulling my hair out!

Thanks in advance,
Mamabear

 

[Deleted member 4993]

Hi, my son's maths assignment is proving to be a challenge and I need help understanding something please. I apologise if this will be a long post!

1) Mrs Jones takes 2 min to walk to her car, 30 sec to get out of the gate, drives 1 km at 40 kmh and then takes 2 minutes to find a park and another minute to walk from the parking space.

Our answer is 5.5 minutes plus 1.5 minutes for driving the 1 km which gives us 7 minutes in total. We added up the time it took doing everything and then went 60 divided by 40 to give us the 1.5 minutes to drive the 1 km. Using Time = Distance/Speed means that we have to divide 1km by 40?

2) Mrs Smith walks to the shops and only has to walk 650 metres. How fast would she have to walk to beat Mrs Jones to the shops?

We have no idea how to work this out given just one bit of information. We think it takes Mrs Jones 7 minutes so I am thinking we need Mrs Smith to walk the 650 metre distance in less than 7 minutes but how do we work this out showing the working?

3) A student thinks she can ride faster. She rides at 20 kmh at the same distance of Mrs Smith (650 metres). Will she be the fastest?

Now here we have used the Time = Distance/Speed and get 32.5 but logically speaking if she can ride 20km in one hour, she can ride 650 metres in 1 minutes and 57 seconds. We don't know which is the correct answer or working out.

I am so confused as to if the answer is 1.57 minutes or 32.5????

I hope someone can help me understand this as I am pulling my hair out!

Thanks in advance,
Mamabear

1) Mrs Jones takes 2 min to walk to her car, 30 sec to get out of the gate, drives 1 km at 40 kmh and then takes 2 minutes to find a park and another minute to walk from the parking space.

There is no question here (in part 1 - only information). We have to organize the information:

Walk to car - 120 sec
get out of gate - 30 sec
drive time = (= distance/speed) = 1/40 hour = 90 sec
park time = 120 sec
Walk to shop = 60 sec
Total time taken by Mrs. Jones = (120+30+90+120+60) = 420 sec

2) Mrs Smith walks to the shops and only has to walk 650 metres. How fast would she have to walk to beat Mrs Jones to the shops?

If Mrs. Smith takes 420 secs to walk 650 meters. Average speed of Mrs. Smith = 650/420 m/s = 0.65 * 60/7 km/h = 5.57 km/h ...... so Mrs smith has to walk faster than 5.57 km/h

3) If Mrs. Smith decides to drive at 20 km/h (assuming all the extra-time like walking to car, parking the car, etc. takes same amount of time) then Mrs. Smith would take:

Walk to car - 120 sec
get out of gate - 30 sec
drive time = (= distance/speed) = 0.65/20 hour = 117 sec
park time = 120 sec
Walk to shop = 60 sec
Total time taken by Mrs. Jones = (120+30+117+120+60) = 467 sec

With the assumptions I made, Mrs. Jones will still win .....

 

[Mamabear]

1) Mrs Jones takes 2 min to walk to her car, 30 sec to get out of the gate, drives 1 km at 40 kmh and then takes 2 minutes to find a park and another minute to walk from the parking space.

There is no question here (in part 1 - only information). We have to organize the information:

Walk to car - 120 sec
get out of gate - 30 sec
drive time = (= distance/speed) = 1/40 hour = 90 sec
park time = 120 sec
Walk to shop = 60 sec
Total time taken by Mrs. Jones = (120+30+90+120+60) = 420 sec

2) Mrs Smith walks to the shops and only has to walk 650 metres. How fast would she have to walk to beat Mrs Jones to the shops?

If Mrs. Smith takes 420 secs to walk 650 meters. Average speed of Mrs. Smith = 650/420 m/s = 0.65 * 60/7 km/h = 5.57 km/h ...... so Mrs smith has to walk faster than 5.57 km/h

3) If Mrs. Smith decides to drive at 20 km/h (assuming all the extra-time like walking to car, parking the car, etc. takes same amount of time) then Mrs. Smith would take:

Walk to car - 120 sec
get out of gate - 30 sec
drive time = (= distance/speed) = 0.65/20 hour = 117 sec
park time = 120 sec
Walk to shop = 60 sec
Total time taken by Mrs. Jones = (120+30+117+120+60) = 467 sec

With the assumptions I made, Mrs. Jones will still win .....

Thank you for replying and for explaining that we need to work out 1) in seconds. I am still confused if we worked out 3) correctly as we have to show the working out to see if the student could be faster than Mrs Jones. Did we do that correctly? If we do time = distance/speed (650/20) we get 32.5 seconds. But logically speaking if she can ride 20kmh, she can ride 650 metres in 1.57 minutes? My son had a relief teacher yesterday who could not explain any of this to him and I am of no help either. This baffles me as using online speed distance and time calculators we got different answers to using my son's calculator and obviously my mind has missed something which is probably very simple!

Thank you once again!!!

Edited: The assignment was 8 pages on Ratios and Speed, Distance and Time and was handed in this morning. I don't think that my son has his answers correct as he has trouble understanding maths but at least it's been handed in. This was the only page that my son couldn't do (or couldn't do with me explaining it step by step as he struggles with maths) and going through his books there was no explanation like yours and no explanation at all about how to work out how fast Mrs Smith could walk to beat Mrs Jones.

Being that I like to know how things are done, I would like to be able to do this for my own knowledge and to see if I am doing it right as it's been a long time since I was at school and I have forgotten a lot of things. I have printed out his assignment and am going to go over it with him on the weekend to hopefully get him to understand it all a bit better as he was just too confused so we just stuck with his answers. If he gets them wrong then so be it and we can just learn from it. Sorry if I come across totally ignorant, this is not my strong point and I have been trying to work it out over 2 days and nights!

Thank you for taking the time to help!

 

[ksdhart2]

It seems to me that the bulk of your confusion over "is it 32.5 or 1.57" is due to neglect of units. The student rides at 20 km/h, that is 20 kilometers per hour. They ride for a distance of 650 meters. Using the distance = speed * time formula will absolutely work in this case, but not if the distance and the speed are in different units. You can either convert the speed to meters or convert the distance to kilometers.

Doing the former gives you: Time (Unknown, but the units will be in hours) = Distance (650 meters) / Speed (20000 meters per hour), for an answer of 0.0325 hours. In minutes, that is 0.0325 * 60 = 1.95 minutes.

Doing the latter gives you: Time (Unknown, but the units will be in hours) = Distance (0.65 kilometers) / Speed (20 kilometers per hour), which also produces the answer of 0.0325 hours or 1.95 minutes.

You absolutely must take caution with units. They cannot be ignored.