Bertie makes payments into a savings account every month. He pays in £300 in the first month and the amount he pays increases by £x x\,x each subsequent month. Charlotte also makes payments into a savings account. She pays in £500 in the first month and the amount she pays in increases by £20 each subsequent month.
After 21 months Bertie and Charlotte have paid in the same amount in total.
Find the value of xxx.
326 exam-style questions on Edexcel A Level Maths Sequences and Series, covering 3.1 Arithmetic Sequences, 3.2 Arithmetic Series, 3.3 Geometric Sequences, 3.4 Geometric Series, 3.5 Sum to Infinity, 3.6 Sigma Notation, 3.7 Recurrence Relations, and 3.8 Modelling with Series. Each one has a worked solution and a mark scheme showing where the marks go.