Use the growth chart to answer the following: Write down, in inches, the measurement of the boy at 9 months.

Step 1: Read the measures from the Length-for-age and Weight-for-age percentiles chart for boys at 9 months.

The plotted point for length-for-age is at 28 inches on the vertical axis.

The plotted point for weight-for-age is at 18 pounds on the vertical axis.

The length is 28 inches and the weight is 18 pounds.

$\boxed{Length = 28 inches, Weight = 18 pounds}$

Step 2: Identify the measure for which the boy has a low percentile.

On the Length-for-age and Weight-for-age chart at 9 months, the length point is near the 50th percentile line (average).

The weight point is below the 10th percentile line (low).

The measure is weight-for-age.

Weight-for-age

Step 3: Estimate the weight-for-length percentile from the Weight-for-length percentiles chart.

The plotted point using length = 28 inches and weight = 18 pounds lies between the 3rd and 5th percentile curves.

The percentile is approximately the 5th percentile.

Approximately the 5th percentile

$\boxed{5th percentile}$

Step 4: State whether the weight-for-length percentile is low.

The 5th percentile is below the 10th percentile, which indicates low.

The percentile is low.