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.

10.9 in.

9.5 in.

12.7 in.

11.2 in.

1 answer

Since the distance a spring stretches varies directly with the weight attached, 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.

From the problem, we know:

  • \( d_1 = 11 \) inches when \( w_1 = 75 \) pounds
  • We want to find \( d_2 \) when \( w_2 = 65 \) pounds

Using the direct variation, we have the proportion:

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

Substituting in the known values:

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

To solve for \( d_2 \), we cross multiply:

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

\[ 715 = 75 \cdot d_2 \]

Now, divide both sides by 75:

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

Calculating \( d_2 \):

\[ d_2 \approx 9.4667 \]

Rounding to the nearest tenth:

\[ d_2 \approx 9.5 \text{ inches} \]

Thus, the spring will stretch approximately 9.5 in.