Question

Express the sum without using summation notation. 5 9 i=1 O 1+ 2+ 3+ 4+ 5 O 9 + 9 + 9 + 9 + 9 O 9 + 18 + 27 + 36 + 45 O 9 + 45

Answer 1

The summation notation tells us

• Take the sum from i = 1 to i = 5

,

• The formula is "9i"

So basically we plug in "1" into "i" of the formula, sum it up with plugging in "2" into i of the formula. Then sum it up with plugging in "3" into i of the formula and so on until 5.

Hence, it will be:

$\begin{gathered} 9(1)+9(2)+9(3)+9(4)+9(5) \\ =9+18+27+36+45 \end{gathered}$

THe third answer choice is right.