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FSMQ Question

I know this question looks really easy, but I can never seem to get the right answer 😭, OK here goes:

Question: John drives along a straight motorway at a constant speed for 120 kilometres. The next day he completes the same journey travelling at 10 km/h faster. He completes this journey in 10 minutes less than the first journey. Find the two speeds at which he travelled.

N.B. The answer you SHOULD get is 80 km/h and 90 km/h

Please help!

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Reply 1
Avatar for Smaug123
Smaug123
15
Original post by Brainiac_98
I know this question looks really easy, but I can never seem to get the right answer ������, OK here goes:

Question: John drives along a straight motorway at a constant speed for 120 kilometres. The next day he completes the same journey travelling at 10 km/h faster. He completes this journey in 10 minutes less than the first journey. Find the two speeds at which he travelled.

N.B. The answer you SHOULD get is 80 km/h and 90 km/h

Please help!

Posted from TSR Mobile

The distance each time was 120km. Say the first day's speed was v_1, so v_1 = 120/t_1. The second day's speed was v_1+10 ("10 km/h faster"), and v_1+10 = 120/(t_1-10), since t_2 = t_1 - 10 ("ten minutes less than the first journey").
Solve those two simultaneous equations.

EDIT: Ah, the second 10 should be 1/6, as brianeverit points out below.
(edited 10 years ago)
Reply 2
Avatar for Brainiac_98
Brainiac_98
OP
3
Soz, I've tried, but I really don't seem to be able to get to the answer, if u could possibly show me how you would get to the answer, then I'd be really grateful :smile:
Original post by Brainiac_98
Soz, I've tried, but I really don't seem to be able to get to the answer, if u could possibly show me how you would get to the answer, then I'd be really grateful :smile:


Set up your equations and solve simultaneously.

Smaug has already given the equations so all you need to do is solve them.

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Reply 4
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Brainiac_98
OP
3
And I said that I tried, but I seem to be getting every answer BUT 80 & 90km/h so that's why I asked for his method...
Reply 5
Avatar for Smaug123
Smaug123
15
Original post by Brainiac_98
And I said that I tried, but I seem to be getting every answer BUT 80 & 90km/h so that's why I asked for his method...

Can you demonstrate how?
Original post by Smaug123
Can you demonstrate how?


Smaug is correct except for saying t_2=t_1-10, it should be t_2=t_1-1/6.
You cannot mix speed in km/h and time in minutes.
(edited 10 years ago)
Reply 7
Avatar for Smaug123
Smaug123
15
Original post by brianeverit
Smaug is correct except for saying t_2=t_1-10, it should be t_2=t_1-1/6.
You cannot mix speed in km/h and time in minutes.

Aargh, I always hated those questions whose main component is making sure you aren't tricked by the malicious question-writers :frown:
Reply 8
Avatar for Brainiac_98
Brainiac_98
OP
3
Ahhhh, thank you! That's what was the problem, got the right answer now!
Original post by Brainiac_98
Ahhhh, thank you! That's what was the problem, got the right answer now!


Glad to help.

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