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3.3.1 Sequences and series (A-level only)

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Question 24

The volume of water VnV_nVn​ (in megalitres) in a reservoir at the end of year n n\,n is modeled by the recurrence relation Vn+1=kVn+50V_{n+1} = kV_n + 50Vn+1​=kVn​+50, where k k\,k is a constant and V1=200V_1 = 200V1​=200.

a.

Find an expression, in terms of kkk, for the volume V2V_2V2​.

[1]
bi.

It is given that the volume at the end of the third year is V3=152V_3 = 152V3​=152 megalitres.

Show that k k\,k satisfies the equation 100k2+25k−51=0100k^2 + 25k - 51 = 0100k2+25k−51=0.

[2]
bii.

Given that the volume of the reservoir is strictly decreasing year-on-year, find the value of V4 V_4\,V4​ and the value of V5V_5V5​.

[3]
ci.

The volume of water in the reservoir approaches a limit L L\,L as n→∞n \rightarrow \inftyn→∞.

Write down an equation for LLL.

[1]
cii.

Find the value of LLL.

[1]

3.3.1 Sequences and series (A-level only) Questions

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