Question 0420

Arithmetic and Geometric Progressions (APs, GPs)

2020 Paper 1 Question 8 Variant

Question

(a)

The 1st term of an arithmetic series is

{4}

and the 8th term is

{3.}

(ai)

Find the 18th term of the series.

[2]

(aii)

Find the sum of the 81st term to the 100th term inclusive of the series.

[3]

(b)

The 1st term of a geometric series is

{4}

and the 8th term is

{\frac{65536}{78125}}

where the common ratio is positive.

(bi)

Find the sum to infinity of the series.

[2]

(bii)

Given that the sum of the first

{n}

terms is greater than

{17.2}

, show that

0.8^n < 0.14.

Hence find the smallest possible value of

{n.}

[5]