How many percent is this shoe on sale/discount?

1)How many percent is this shoe on sale/discount?
2) I buy him toy as motivation to study harder.
3) I set a few different alarms on my phone that go off at different time.
4)I set a few different alarms on my phone that go off at 5 minutes interval.

Are the above sentences correct? Please advice.

  1. What percentage discount is available on this shoe?
  2. I buy (am buying/will buy) him a toy as motivation to study harder.
  3. I have set a few different alarms on my phone that go off at different times.
  4. I have set the alarm on my phone to go off at 5 minute intervals.