Question

A jogger runs 300 m in the fi rst minute.
The distance the jogger covers decreases
by 20 m in each succeeding minute.
What distance does the jogger cover in
the 7th minute?
How do I come up with an equation?

Answer 1

making a table can help:
min distance
1 300m
2 300-20
3 300-20-20
4 300-20-20-20

we can see that
at 2 min we subtract one twenty
at 3 min we subtract two twenties
at 4 min we subtract three twenties.

total distance = 300m - 20*minutes beyond 1 minute

becomes
total distance = 300m - 20(min - 1)
or
distance = 300 - 20(t-1); where t is time.

Answer 2

but doesn't that mean that the jogger covers 280m in the second minute? shouldn't that be 580m?

Answer 3

shoot
yes, you are right, sorry
I did the arithmetic term,

to get the sum, we have to use the arithetric sum formula,
so,
d =(t/2)*(2*300-20*(t-1))


sorry about that

Answer 4

thanks for your help!