Question

Three girls, Laura, Tammy, and Jeri, can wash the family cars, clean the pool, and mow the lawn in one hour and 20 minutes. If Jeri did all the work, she would take twice as long as Tammy and 2 hours longer than Laura. How long would Tammy take to do the job alone?
3 hrs.
4 hrs.
6 hrs.

Answer 1

Laura DATA:
Time = x hr/job ; Rate = 1/x job/hr
Jeri DATA
Time = x+2 hr/job ; Rate = 1/(x+2) job/hr
Tammy DATA:
Time = (x+2)/2 hr/job ; Rate = 2/(x+2) job/hr.
Together DATA:
time = 4/3 hr/job ; Rate = 3/4 job/hr
EQUATION:
rate + rate + rate = together rate
1/x + 1/(x+2) + 2/(x+2) = 3/4
Multiply thru by 4x(x+2) to get:
4(x+2) + 4x + 8x = 3x(x+2)
16x + 8 = 3x^2+6x
3x^2-10x-8 = 0
3x^2-12x+2x-8 = 0
3x(x-4)+2(x-4) = 0
(x-4)(3x+2) = 0
Positive answer:
x = 4 hrs. time for Laura to do the job
x+2=6 hrs. time for Jeri to do the job
(x+2)/2 = 3 hrs. time for Tammy to do the job