as given that The first day, she will complete 10 sit-ups. Every day she will do twice as many sit-ups as the
day before.
So at first day: a=10
On second day: b=2a
On third day: c=2b
on 4th day: d=2c
So when we arrange it in a order
[tex]\begin{gathered} a,b,c,d\ldots\text{.} \\ a,2a,2b,2c\ldots\text{.} \\ a,2a,2(2a),2(2(2a)\ldots\text{.} \\ a,2a,4a,8a\ldots \end{gathered}[/tex]And the value of a=10: so
[tex]10,20,40,80,\ldots\text{..}[/tex]