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 Post subject: Distance questionPosted: Wed Jun 17, 2020 2:09 pm

Joined: Sat Jun 30, 2018 12:46 pm
Posts: 89
Hi, if anyone is able to explain how I get to this answer, I'd appreciate it please?

Four cars take part in a long distance road race. The total distance to be covered is 153 kilometers. The average speed of the cars is shown in the table below in kilometers per hour.

Car A - 96kmh
Car B - 60kmh
Car C - 108kmp
Car D - 84kmp

What distance has the slowest car in the race covered when the fastest car crosses the finish line?

A - 91KM
B - 85KM
C - 88KM
D - 95KM
E - 80KM

The answer is 85km with the explanation of: The speed of the fastest car is 108kmph. Time taken by fastest car to complete the race = 153 / 108 = 1 hours 25 min. The speed of the lowest car is 60kmph. Distance covered by the slowest car in the same time = 85km.

It's probably a simple explanation but I can't see it.

Thank you.

Last edited by ciaowood on Wed Jun 17, 2020 5:55 pm, edited 1 time in total.

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 4:07 pm

Joined: Wed May 09, 2007 3:09 pm
Posts: 1206
Location: Solihull, West Midlands
You just need to remember that Speed = Distance divided by time

which means Speed x time = distance

and also time = distance divided by speed

So if you know any two of the three you can find the other (and remember to check the units, including 60 minutes in an hour! )

This triangle might help (used a lot in remembering such simple formulae)

https://owlcation.com/stem/Using-the-ma ... d-measures

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 4:08 pm

Joined: Wed May 09, 2007 3:09 pm
Posts: 1206
Location: Solihull, West Midlands
(deleted to remove duplicate!)

Last edited by solimum on Wed Jun 17, 2020 4:17 pm, edited 1 time in total.

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 4:08 pm

Joined: Wed Dec 05, 2018 11:16 pm
Posts: 8
As distance is speed x time. The slowest car is travelling at 60kmph or 1 km per minute
The distance the slowest car covers in 1 hour 25 mins or 85 mins will be 85km
Hope that helps

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 5:34 pm

Joined: Sat Jun 30, 2018 12:46 pm
Posts: 89
Thanks both, I'm clearly not familiar with this formula so I know what I'm doing tonight

Appreciate your help with this - thanks.

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 7:18 pm

Joined: Sat Jun 30, 2018 12:46 pm
Posts: 89
I'm struggling! I can't see how 153/108 = 1hr 25m, can anyone help please?

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 7:55 pm

Joined: Wed May 09, 2007 3:09 pm
Posts: 1206
Location: Solihull, West Midlands
It's a bit nasty I agree, but persevere

153/108 = 1.41666667 as a decimal

Or simplifying the fraction (noticing they both are divisible by 9) = 17/12 = 1 + 5/12

1/12 of an hour is 5 minutes

So 17/12 of an hour is 1 hour plus another 25 minutes

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 8:54 pm

Joined: Sat Jun 30, 2018 12:46 pm
Posts: 89
Fabulously explained, thank you so much!

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 11:46 pm

Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
This is not an appropriate 11+ question.

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 Post subject: Re: Distance questionPosted: Wed Jun 17, 2020 11:47 pm

Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
solimum wrote:

This triangle might help (used a lot in remembering such simple formulae)

https://owlcation.com/stem/Using-the-ma ... d-measures

NEVER teach this to children please.

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