A can complete a piece of work in 21 hours. With the help of A, B can do it in 6 1/4 hrs. less time than he could do it alone. How many hrs. does B need to do it alone? What kind of equation do you need to solve this problem?

- stapel_eliz
**Posts:**1628**Joined:**Mon Dec 08, 2008 4:22 pm-
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To learn how to set up and solve this sort of exercise, please tryA can complete a piece of work in 21 hours. With the help of A, B can do it in 6 1/4 hrs. less time than he could do it alone. How many hrs. does B need to do it alone? What kind of equation do you need to solve this problem?

Then use the set-up explained and demonstrated in the lesson:

. .. .time to complete task (hours):

. . . . .A: 21

. . . . .B: b

. . . . .together: b - 6.25

. . .completed per time unit (hours):

. . . . .A: 1/21

. . . . .B: 1/b

. . . . .together: ...

...and so forth.

I used this equation: 1/21 +1/b = 1/b-6.25, tried to have it worked out on Mathway and was told it had no solution.

- stapel_eliz
**Posts:**1628**Joined:**Mon Dec 08, 2008 4:22 pm-
**Contact:**

If you entered the equation as you've posted above (that is, without grouping symbols for the denominator on the right-hand side), then there clearly is no solution.I used this equation: 1/21 +1/b = 1/b-6.25, tried to have it worked out on Mathway and was told it had no solution.

However, if you multiply through to clear the denominators, you will find that you get a quadratic equation that is quite solveable.