Here is your answer
Money saved on each successive day is-
$3, &5, $7....
Clearly it forms an AP,
where
a1= 3
common difference, d= 2
n=20
So,
using formula
Tn= a1+(n-1)d
T20= 3+(20-1)2
= 3+ 19×2
= 3+ 38
=41
So, money saved on August 20= $41
Sum of money saved upto August 20 =
n/2 (a1+T20)
= 20/2 (3+41)
= 10× 44
= $440
HOPE IT IS USEFUL
