What is the 5th term of the G.P. 5, 10, 20, ...?
Answer: C
In this G.P., the first term \(a = 5\) and the common ratio \(r = 10/5 = 2\). The formula for the nth term is \(a_n = ar^{n-1}\). For the 5th term (n=5), we have \(a_5 = 5 \times 2^{5-1} = 5 \times 2^4 = 5 \times 16 = 80\).