Kevin can make 10 widgets in 7 hours and David can make 12 widgets in 5 hours. How many

hours are needed for them to make 67 widgets together?

17.5 hours or 17 h 30 min

Step-by-step explanation:

Kevin makes (10/7) widgets per hour.

David makes (12/5) widgets per hour.

Together they make

(10/7 + 12/5) widgets per hour.

Also, they make 67 widgets for x hours.

So, they can make 67/x widgets per hour.

10/7 + 12/5 = 67/x

(10*5) / (7*5) + (12*7) / (5*7) = 67/x

50/35 + 84/35 = 67/x

134/35 = 67/x

134x = 35*67

x = 35*67/134 = 17.5 h