Mai is participating in a 4-day cross-country biking challenge. She biked for 55, 60, and 50 miles on the first three days. How many miles does she need to bike on the last day so that her average (mean) is 55 miles per day?

Answer 1

To find out how many miles Mai needs to bike on the last day to have an average of 55 miles per day over the 4 days, we can use the following steps:

1. Calculate the total distance needed for the 4 days: The average distance Mai wants to bike is 55 miles per day. Over 4 days, the total distance she needs to bike is: \[ 55 \text{ miles/day} \times 4 \text{ days} = 220 \text{ miles} \]

2. Calculate the total distance biked in the first 3 days: Mai biked:

   • Day 1: 55 miles
   • Day 2: 60 miles
   • Day 3: 50 miles

   Adding these distances together gives: \[ 55 + 60 + 50 = 165 \text{ miles} \]

3. Determine the distance needed on the last day: Let \( x \) be the distance Mai needs to bike on the last day. To find \( x \), we set up the equation: \[ 165 + x = 220 \] Solving for \( x \): \[ x = 220 - 165 = 55 \text{ miles} \]

Thus, Mai needs to bike 55 miles on the last day to achieve her goal of averaging 55 miles per day.