It would be 400 if you're counting by tens
Distance formula is SquareRoot of (x2-x1)^2 + (y2-y1)^2
= SQRT( (8-0)^2 + (-8-7)^2 )
=SQRT(64 +225)
=SQRT(289)
= 17
The probability of getting all heads is 1/2
there is two sides, one head an one tail, or 1/2 chance of getting heads
Tossed 10 times, it still has 1/2
hope this helps