A robotic printing head deposits layers of concrete to form a structural support pillar. The first layer has a thickness of 15.0 mm. Each subsequent layer is 2.5 mm thicker than the layer immediately preceding it. This process continues until the total height of the pillar reaches a specific requirement.
(i) State, with a reason, whether an arithmetic series or a geometric series should be used to model the thickness of the layers.
(ii) Determine an expression for the thickness of the nnn-th layer, TnT_nTn, in terms of nnn.
Given that the final height of the pillar must be at least 2100 mm, calculate the minimum number of layers required to complete the pillar.
231 exam-style questions on WJEC A Level Maths 3.4 Sequences and Series (A-level only), covering 3.4.1 Sequences and Series (A-level only), 3.4.2 Sequences and Series (A-level only), 3.4.3 Sequences and Series (A-level only), 3.4.4 Sequences and Series (A-level only), 3.4.5 Sequences and Series (A-level only), 3.4.6 Sequences and Series (A-level only), and 3.4.7 Sequences and Series (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.