Which of the following is the expanded form of ?

MATHEMATICS · Single correct · A Level · Mathematics · Sequences and series · Sequences and series

Problem

Which of the following is the expanded form of

\displaystyle\sum_{r=1}^{5} 4\cdot 2^{\,r-1}

? (a)

8 + 16 + 32 + 64 + 128

(b)

4 + 8 + 16 + 32

(c)

4 + 8 + 16 + 32 + 64

(d)

4 + 8 + 16 + 32 + 64 + 128