SOLUTION: Hi I'm stuck on this question: On Monday William spends 20mins playing the piano. On Tuesday 25 minutes and on each successive day his playing time increases in the same ratio.

Algebra ->  Sequences-and-series -> SOLUTION: Hi I'm stuck on this question: On Monday William spends 20mins playing the piano. On Tuesday 25 minutes and on each successive day his playing time increases in the same ratio.       Log On


   

Question 1108381: Hi I'm stuck on this question:
On Monday William spends 20mins playing the piano. On Tuesday 25 minutes and on each successive day his playing time increases in the same ratio. How many minutes does he play on Friday?
// I've tried doing the question "the long way" but at school, we're focusing on geometric series hence can you show me how to do this question using relevant formulas from this topic. //
Thankyou in advance
Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


It's the basic formula for a geometric sequence: the n-th term is the first term, multiplied by the common ratio (n-1) times.

He played for 20 minutes on Monday and 25 minutes on Tuesday. So the first term is 20 and the common ratio is 25/20 = 5/4.

Friday will be the 5th term of the sequence, so the number of minutes he will play on Friday is 20%2A%285%2F4%29%5E4+=+20%2A%28625%2F256%29+=+5%2A625%2F64+=+3125%2F64