Half life help!

Question

The remaining amount of a strontium -90 that has had 5 half- lives pass is 25.0 g. How much was present at the beginning? Round to the correct number of significant figures and use units (g)

Answer 1

800 grams was the original amount.

five half lives and half life can be represented by 2 and we raise the 2 ^5 2^5 = 32 and I multiplied 25 x 32 and got 800 grams