Common ratio

If 200 units of a commodity are consumed in a first year, and if the annual rate of increase in consumption is 5%

(a) what amount is consumed in the 8th year;
(b) in the first 15 years?

Correct result:

a8 =  281.4201
s15 =  4315.7127

Solution:

a1=200 q=5%=1+5100=1.05  a8=a1⋅ q8−1=200⋅ 1.058−1=281.4201
s15=a1⋅ q15−1q−1=200⋅ 1.0515−11.05−1=4315.7127

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