Question 324511
Two scenarios:
First, you must get the seven digits exactly as drawn. 
Example: 1234567 is drawn, your ticket 7654321 would not win since they're not in the correct order.
You have a permutation without repetition.
{{{ N=10!/(10-7)! }}}
{{{N=10!/3!}}}
{{{N=10*9*8*7*6*5*4=604800}}}
{{{P=1/N=1/604800}}}
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Second, order doesn't matter. In the example above, you'd be a winner.
You have a combination without repetition.
{{{N=10!/(7!(10-7)!)}}}
{{{N=10!/(7!3!)}}}
{{{N=(10*9*8)/(3*2*1)=120}}}
{{{P=1/120}}}