露丝（Ruth）需要90段长度各为 $\frac{4}{5}$ 米的丝带装饰房间。丝带每卷长10米。

1. Divide the total length of one roll by the length of one piece

$10 \div \frac{4}{5} = 10 \times \frac{5}{4} = \frac{50}{4} = 12.5$

2. Determine the maximum number of whole pieces

Since Ruth can only get whole pieces of ribbon, we round down to the nearest whole number.
Maximum number of pieces = $12$

1. Determine the number of pieces of ribbon that can be cut from one roll (from part a)

Number of pieces per roll $= 10 \div \frac{4}{5} = 10 \times \frac{5}{4} = 12.5$
Since she can only get whole pieces, $1$ roll provides $12$ pieces.

2. Calculate the number of rolls needed to get 90 pieces

Number of rolls needed $= 90 \div 12 = 7.5$
Since Ruth must buy whole rolls, she needs to round up to the next whole number.
Least number of rolls $= 8$