Finding an Unknown - Averages

1. Finding an Unknown - Averages • Sometimes, you know the average you want but aren’t quite sure what you need to achieve it. For example: John needs to work an average of 20 hours a week over six weeks to satisfy his scholarship requirement. If he works 35 hours the first week, 20 hours the second week, 10 hours the third week, 22 hours the fourth week and 18 hours the fifth week, how many hours does he need to work on the sixth week to meet the requirement?

2. John needs to work an average of 20 hours a week over six weeks to satisfy his scholarship requirement. If he works 35 hours the first week, 20 hours the second week, 10 hours the third week, 22 hours the fourth week and 18 hours the fifth week, how many hours does he need to work on the sixth week to meet the requirement? • Mathematically it looks like this:

3. Multiply both sides by 6 to get rid of the fraction: x6 x6

4. 35 + 20 + 10 + 22 + 18 + x = 120

5. 35 + 20 + 10 + 22 + 18 + x = 120 105 + x = 120 -105 -105 x = 15 John will have to work 15 hours on the sixth week to meet his requirement.

6. Try the practice problems on page 146 of your book to practice these skills. Check your answers on BB.