Double Strike on opponents (Magic the Gathering)?

Question

I have a creature 5/5 creature with double strike. My opponent chooses not to block with one of his creatures and decides to take the damage instead. How much damage is he dealt?

Answer 1

10 damage is dealt

a double strike creature deals first strike damage AND normal damage.

if your opponent had a 3/3 creature and he blocked, the first strike damage would kill the creature and he would still be dealt 5 damage from the normal damage dealt AFTER first stike and AFTER his blocker dies.

double strike works with ninjitsu

Answer 2

10 damage. Double strike does first strike damage AND normal combat damage. So its like your creature attacked twice.