For every 7 candy bars that Emma sells, Robert sells 2. They sold 81 candy bars altogether last week. How many fewer candy bars did Robert sell than Emma?

Answer 1

E = Emma's candy bars

R = Robert's candy bars

For every 7 candy bars that Emma sells, Robert sells 2 means:

E / R = 7 / 2

Cross multiply

2 E = 7 R

Divide both sides by 2

E = 7 / 2 R

They sold 81 candy bars altogether last week means:

E + R = 81

Replace E with 7 / 2 R in this equation

7 / 2 R + R = 81

7 / 2 R + 2 / 2 R = 81

9 / 2 R = 81

Multiply both sides by 2

9 R = 162

Divide both sides by 9

R = 162 / 9 = 18

Robert sells 18 candy bars

E = 7 / 2 R

E = 7 / 2 • 18 = 126 / 2 = 63

Emma sells 63 candy bars

E - R = 63 - 18 = 45

Robert sell 45 fewer candy bars than Emma