# How to Calculate the Time Taken To Run A 20m Race Using This Formula? ?

d(t) = -(10/t+0.625) + 20

I have to substitute D with this one as well but I found this one even more confusing?

### 8 Answers

- jeffrcalLv 74 months ago
There are no units given in your formula. If the units are assumed to be metres then the formula does not make sense since 20m would have no solutions.

- D gLv 74 months ago
d(t) is the distance at that time

The time will be t2 - t1

d( t2) - d(t1) = 20m I'm assuming distance in meters

Looking at the formula the distance formula is unusual

The distance will only have a limit of 20 m at time = infinity

This suggests the time of the race will be infinitely long

You could start at a different distance which suggests z different time

- ?Lv 74 months ago
Are you sure this formula is correct??

Since d(t) = 20 m, according to the formula,

....................-10

..........20 = ------------- + 20 ⇒

....................t + 0.625

....................-10

..........0 = ------------- ⇒

.................t + 0.625

..........0 = -10 which is INCONSISTENT

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- Engr. RonaldLv 74 months ago
let d(t) = 20m

..............10

20 = - ------------- + 20

............t + 0.625

20(t + 0.625) = - 10 + 20(t + 0.625)

20t + 12.5 = - 10 + 20t + 12.5

20t - 20t = 12.5 - 12.5 - 10

0 = - 10

Therefore there is no solution for this problem..

- Steve4PhysicsLv 74 months ago
Note, 1/2+3 does not mean the same as 1/(2+3). To type out the equation correctly on a single line you need extra brackets:

d(t) = -(10/t+0.625) + 20

should be:

d(t) = -(10/(t+0.625)) + 20

Or even neater:

d(t) = 20 – 10/(t+0.625)

_________________________

It’s a trick question. The race can never be completed with this relationship between d and t.

If you look at the equation:

d(t) = 20 – 10/(t+0.625)

you will see the right hand side is always less than 20, because you are subtracting 10/(t+0.625) from 20.

It would take an infinite amount of time to move 20m. When t equals infinity, 10/(t+0.625) equals zero.

- TomVLv 74 months ago
Taking the image as the correct equation and substituting 20 for d(t), the equation has no finite solution.

20 = -10/(t+0.625) + 20

0 = -10/(t+0.625)

0 = -10

There is no finite value of t that satisfies the equation. Check your presentation of the problem for errors and resubmit.

- SlowfingerLv 64 months ago
The text reads d(t) = -(10/t+0.625) + 20

but the picture shows d(t) = -10/(t+0.625) + 20

Which one is correct?