9.

The distance a spring will stretch varies directly with how much weight is attached to the spring. If a spring stretches 11 inches with 75 pounds attached, how far will it stretch with 65 pounds attached? Round to the nearest tenth of an inch.

1 answer

The relationship between the distance a spring stretches and the weight attached can be represented using the concept of direct variation. This means we can set up a proportion based on the information given.

Let \( d \) be the distance the spring stretches, and \( w \) be the weight attached. We know from the problem that:

\[ d_1 = 11 \text{ inches} \text{ when } w_1 = 75 \text{ pounds} \]

We want to find \( d_2 \) when \( w_2 = 65 \text{ pounds} \). Since the stretching distance varies directly with weight, we can set up the following proportion:

\[ \frac{d_1}{w_1} = \frac{d_2}{w_2} \]

Substituting in the known values:

\[ \frac{11}{75} = \frac{d_2}{65} \]

To find \( d_2 \), we can cross-multiply:

\[ 11 \times 65 = 75 \times d_2 \]

Calculating \( 11 \times 65 \):

\[ 11 \times 65 = 715 \]

So we have:

\[ 715 = 75 \times d_2 \]

Now, we solve for \( d_2 \):

\[ d_2 = \frac{715}{75} \]

Calculating the division:

\[ d_2 \approx 9.4667 \]

Rounding to the nearest tenth of an inch:

\[ d_2 \approx 9.5 \]

Thus, the spring will stretch approximately 9.5 inches with 65 pounds attached.