EXAMPLE 4 Writing and Evaluating an Expression

Heart Rate

a. Use n to write an expression for heart rate in beats per minute.

b. After exercising, you count 24 beats in 15 seconds. Find your heart rate.

To measure your heart rate, count the number of heartbeats n in 15 seconds. Then multiply by 4 to find your heart rate in beats per minute.

EXAMPLE 4 Writing and Evaluating an Expression

SOLUTION

a. The phrase multiply by suggests multiplication. So, multiply the number of heart beats n by 4.

ANSWER A variable expression for heart rate in beats per minute is 4n.

b. Substitute 24 for n in the expression 4n to find your heart rate.

4n = 4(24) = 96

ANSWER Your heart rate is 96 beats per minute.

GUIDED PRACTICE for Example 4

10. Savings You have $25 saved. You save $4 more per week for n weeks. Write and evaluate an expression for your total savings after 8 weeks.

= 25 + 4n

= 25 + 4(8)

= 57

SOLUTION

ANSWER

Total saving after 8 weeks is $57