Help Please!!!

If your allowance double every week, then it was 1/2 as much last week.

Since it is 2.56 now, it was (1/2)x(2.56)  =  1.28 last week.

The week before, it was (1/2)x(1.28)  =  0.64.

And, the week before that, it was (1/2)(0.64)  =  0.32.

So, three weeks ago, it was  0.32.

2.56 x 2^-3=.32 your allowance 3 weeks ago.

$0.32