The systolic blood pressure of adults in the USA is nearly normally distributed with a mean of 121 and standard deviation of 18 . Someone qualifies as having Stage 2 high blood pressure if their systolic blood pressure is 160 or higher. a. Around what percentage of adults in the USA have stage 2 high blood pressure? Give your answer rounded to two decimal places. $\%$

Step 1 ：Given that the mean systolic blood pressure of adults in the USA is \(121\) and the standard deviation is \(18\).

Step 2 ：We are asked to find the percentage of adults with a systolic blood pressure of \(160\) or higher, which qualifies as Stage 2 high blood pressure.

Step 3 ：We can solve this problem using the concept of Z-score in statistics. The Z-score is a measure of how many standard deviations an element is from the mean.

Step 4 ：First, we calculate the Z-score for a blood pressure of \(160\) using the formula \(Z = \frac{X - \mu}{\sigma}\), where \(X\) is the value we are interested in, \(\mu\) is the mean, and \(\sigma\) is the standard deviation.

Step 5 ：Substituting the given values, we get \(Z = \frac{160 - 121}{18} = 2.1666666666666665\).

Step 6 ：Next, we find the area under the normal distribution curve that is to the right of this Z-score. This area represents the percentage of adults with stage 2 high blood pressure.

Step 7 ：Using a standard normal distribution table or a calculator, we find that the area to the right of \(Z = 2.1666666666666665\) is approximately \(0.0151\) or \(1.51\%\).

Step 8 ：\(\boxed{\text{Final Answer: Around 1.51% of adults in the USA have stage 2 high blood pressure.}}\)