Exercise 49 Page 415

Let's start by recalling the formula for this special series. Sum ofn terms of1 ∑_(i=1)^n 1 = n Let's now consider the given series. ∑_(i=10)^(25) 1 Here we have that n = 25. Therefore, to find the desired sum we will substitute 25 for n in the corresponding formula.

∑_(i=1)^n 1 = n

Substitute

n= 25

∑_(i=1)^(25) 1 = 25

We need to keep in mind that the sum starts with 10, so we need to subtract 9 from the previously calculated number. ∑_(i=10)^(25) 1 = 25- 9=16