1. What are the last two digits of 9^2013?

2. Show that 5^t=2 + 3(5^t+1) - 40(5^t) is equal to zero.

3. Under certain conditions, I = 10^D/10 where D is the number of decibels of a sound and I is its intensity. If he shouts with 30 more decibels that she talks with, what is the ratio of his intensity to hers?

Show that 5^t=2 + 3(5^t+1) - 40(5^t) is equal to zero.

I don't believe it is. Let t=0, then
1=2+3(1+1)-40*1 which is not true.