A painter can finish painting a house in 7 hours. Her assistant takes 9 hours to finish the same job. How long would it take for them to complete the job if they were working together?

c =3.9375 hours

Step-by-step explanation:

The formula to determine time to finish the job together is

1/a + 1/b = 1/c

Where a and b are the times to complete the job separately and c is the time to complete the job when working together

1/7 + 1/9 = 1/c

Multiply by 63c to get rid of the fractions

63c*(1/7 + 1/9) = 1/c *63c

9c + 7c = 63

Combine like terms

16c = 63

Divide each side by 16

16c/16 = 63/16

c =3.9375 hours

3.9375 hours

Step-by-step explanation:

Combined time

= product of individual times ÷ sum

= (7×9)/(7+9)

= 63/16

= 3.9375

7. d. 64

8. i. 32

9. c. 125

10. j. none of the above

11. d. 81

12. i. 216

13. e. none of the above

14. g. 240

15. e. none of the above

16. g. 32

17.   e. none of the above