How can I get a better understanding of word problems????

Question

Eugene can dig a 10 ft by 10 ft in nine hours. Molly can dig the same hole in seven hours. How long would it take if they worked together? please i need help can someone explain to me how to solve!!

Answer 1

Eugene does 1/9 of the job in one hour

Molly does 1/7 of the job in one hour

x=# of hours working together to do the job

(1/9)x+(1/7)x=1 (job finished)

multiply both sides by 63

63(1/9)x+63(1/7)x=63(1)

7x+9x=63

16x=63

x=63/16

x=3.9375 hours or 3 15/16 hours working together

check: (1/9)(3.9375)=0.4375 of the job done by Eugene

           (1/7)(3.9375)=0.5625 of the job done by Molly

            0.4375+0.5625=1 (job finished)

Answer 2

Great answer Arthur.