I used to be able to do these

@iamatiger said
@Eladar

No probs eladar, I like these puzzles venda!

Yeah, you have good number sense and reasoning. Way better than most.

Any particular reason you chose 13?

People generally enjoy what they are good at.

@iamatiger said
@Eladar

No probs eladar, I like these puzzles venda!

Thanks for that tiger.
As I thought there is a trial and error element but the clues are there to lead you in the right direction.
As you like this sort of thing, here's another:-
2 cars set off from the same point to travel the same journey
The first car has a 9 minute start.
The first car travels at 80km/h
The second car travels at 95km/h
How many km from the start will the cars draw level?

@venda said
Thanks for that tiger.
As I thought there is a trial and error element but the clues are there to lead you in the right direction.
As you like this sort of thing, here's another:-
2 cars set off from the same point to travel the same journey
The first car has a 9 minute start.
The first car travels at 80km/h
The second car travels at 95km/h
How many km from the start will the cars draw level?

That one is a much easier question.

9 min is .15 hours

80×.15 is 12, so the first car has a 12 km lead.

The second car is traveling 15 km per hour faster than the first. Using d= rt...
12=15t and solving for t you get .8 hours.

.8 hours is 40 minutes.

@eladar said
That one is a much easier question.

9 min is .15 hours

80×.15 is 12, so the first car has a 12 km lead.

The second car is traveling 15 km per hour faster than the first. Using d= rt...
12=15t and solving for t you get .8 hours.

.8 hours is 40 minutes.

Maybe so.
But that is not the question.
The answer is the distance travelled when the cars are level

@venda

Well if it takes 40 min to be even then multiply .8 by the speed of the second car.

95 x.8 =76 km.

So yeah always make sure you are answering the question.

@eladar said
@venda

Well if it takes 40 min to be even then multiply .8 by the speed of the second car.

95 x.8 =76 km.

So yeah always make sure you are answering the question.

Yes.
Well done

@venda
D= S1 * S2 * t / (S1 - S2)
D= 90 * 80 * 9/60 /15
D= 90*80*9/(60*15)
D= 90*8*9/(6*15)
D= 90*8*9/90
D=8*9
D=72

@iamatiger

Cool formula. What is it based on?

t is obviously the difference in starting times not the time one of the cars is traveling.

It gave us different answers.

The slower car doing 80 would be traveling .95 hours also resulting in 76.

Ok found your error. You used 90 km per hour instead of 95.

9.5×8 results in 76

@Eladar

Thanks Eladar, car-less of me!
Formula is that is car at S1 has a head start of t, it goes a distance ofS1*t
The delta speed of the two cars is (S2-S1)
So the time for the second car to catch up is
(S1 * t)/(S2 -S1)
The final distance is S2 * time so we have:
Final distance = D = S1*S2*t/(S2 - S1)

Interestingly this rearranges to
t/D = 1/S1 - 1/S2

@eladar said

.8 hours is 40 minutes.

0.8 hours is 48 minutes.

@wolfgang59 said
0.8 hours is 48 minutes.

Good thing I calculated with hours.

@iamatiger said
@Eladar

Thanks Eladar, car-less of me!
Formula is that is car at S1 has a head start of t, it goes a distance ofS1*t
The delta speed of the two cars is (S2-S1)
So the time for the second car to catch up is
(S1 * t)/(S2 -S1)
The final distance is S2 * time so we have:
Final distance = D = S1*S2*t/(S2 - S1)

Interestingly this rearranges to
t/D = 1/S1 - 1/S2

Yeah thought about it. You just made a formula of the steps I went through. In the US we like to use basic formulas then build answers instead of simplified formulas for specific cases.

Nice pun, just got it lol.

@iamatiger
You're obviously a very qualified mathematician.
What level have you achieved academically?
I detested mathematics at school but later in life my interest was sparked when I saw a problem in a newspaper about someone trying to fill up a bath with the plug out!!(why would yo do that?)
I couldn't work it out and it annoyed me so I got a book out of the library and it all started from there.
People then started buying me mathematical puzzle books for birthdays and xmas which is where most of the ones I put on here come from

@eladar said
Good thing I calculated with hours.

Math teacher lol