Final answer:
To find the infinite geometric sum of the series 80 + 10 + 1.25 + ..., use the formula S = a / (1 - r), with 'a' as the first term and 'r' as the common ratio. Apply the significant figures principle for accurate rounding when approximating to a certain number of decimal places.
Step-by-step explanation:
The student's question involves finding the infinite geometric sum of the series 80 + 10 + 1.25 + .... To determine this sum, we use the formula for the sum of an infinite geometric series, S = a / (1 - r), where 'S' is the sum of the series, 'a' is the first term, and 'r' is the common ratio between terms. In this series, 'a' is 80, and the common ratio 'r' can be found by dividing the second term by the first term, which is 10/80 or 1/8.
Plugging the values into the formula gives us S = 80 / (1 - (1/8)) which simplifies to S = 80 / (7/8) = 80 * (8/7) = 640/7. Calculating this yields an infinite sum which can be approximated to decimal places as needed.
For precise calculations, especially when rounding to a certain number of decimal places or significant figures, the rules of significant figures must be followed. As the sample information shows, if a number in the tenths place is to be dropped and it's greater than 5, we round up to ensure the final value adheres to the significant figures principle, consistently providing a more accurate and professional result.