# Need help plz: Mark arrived at his office at 12 pm. If he had increased his speed...

#### Adam_2016

##### New member
Mark arrived at his office at 12 pm, if he had increased his speed by 5k/h he would arrive 4 min earlier and if he decreases his speed by 5k/h he would arrive 5 min after. The question is at what time he had left his home keeping his speed at original speed?

#### Subhotosh Khan

##### Super Moderator
Staff member
Mark arrived at his office at 12 pm, if he had increased his speed by 5k/h he would arrive 4 min earlier and if he decreases his speed by 5k/h he would arrive 5 min after. The question is at what time he had left his home keeping his speed at original speed?
What are your thoughts regarding the assignment?

Please share your work with us ...even if you know it is wrong.

If you are stuck at the beginning tell us and we'll start with the definitions.

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#### Dr.Peterson

##### Elite Member
Mark arrived at his office at 12 pm, if he had increased his speed by 5k/h he would arrive 4 min earlier and if he decreases his speed by 5k/h he would arrive 5 min after. The question is at what time he had left his home keeping his speed at original speed?
This is most naturally done with algebra. What unknown quantities are there that you can define as variables? What equations can you write to express the facts of the problem?

#### stapel

##### Super Moderator
Staff member
I have moved this question from "Calculus" to "Algebra".

Mark arrived at his office at 12 pm, if he had increased his speed by 5k/h he would arrive 4 min earlier and if he decreases his speed by 5k/h he would arrive 5 min after. The question is at what time he had left his home keeping his speed at original speed?
To learn the basic set-up process for "uniform rate" exercises, please try here. Once you have studied the lesson and learned the basic terms and techniques, please attempt the exercise, starting with:

. . .original:
. . . . .rate: r
. . . . .time: t
. . . . .distance: d = rt

. . .faster:
. . . . .rate: r + 5
. . . . .time: t - 4/60
. . . . .distace: rt = (r + 5)(t - 4/60)

. . .slower:
. . . . .rate: r - 5
. . . . .time: [fill this in]
. . . . .distance: [fill this in]

Then solve for the time "t".

If you get stuck, please reply showing all of your work and reasoning, starting from the above. Thank you!