Question

Order the next expressions of time in ascending order.
Seven days, last year, a year, 9 o'clock, 30 minutes, August, three weeks, 1986, nine months, last summer.
-Classify the above mentioned time expressions according to whether they can be used with 'since' 'for'
For Since

Answer 1

For seven days.
For a year.
For 30 minutes.
For three weeks.
For nine months.

Since last year.
Since 9 o'clock
Since August
Since 1986
Since last summer.

For, lo utilizamos para expresar que cierta cantidad de tiempo o algun evento ha estado suceciendo o sucede. Tambien para expresar tiempo pasado. Ej:

I study for 30 min.
The teacher was on vacation for seven days.

Since, expresa que algun período de tiempo, situación o evento ha estado ocurriendo (en algunos casos ya sucedido, pasado). Lo usamos para decir "desde" literalmente, en algunas expresiones negativas.
Ej

I don't see you since last summer.
She doesn't see her brother since 1986.