SOLUTION: Tom can clean the living room in 45 minutes. Wally can clean it in 30 minutes. If both start cleaning and 5 minutes later, their sister Gigi joins them, taking them 7 minutes more

Question 674178: Tom can clean the living room in 45 minutes. Wally can clean it in 30 minutes. If both start cleaning and 5 minutes later, their sister Gigi joins them, taking them 7 minutes more to finish. How long would it take Gigi to clean the living room alone?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Tom can clean the living room in 45 minutes.
Wally can clean it in 30 minutes.
If both start cleaning and 5 minutes later, their sister Gigi joins them, taking
them 7 minutes more to finish.
How long would it take Gigi to clean the living room alone?
:
let g = Gigi's time to do the job alone (in minutes)
let the completed job = 1 (a spotless living room)
:
A shared work equation. (T and W worked a total of 5+7 = 12 minutes)
+ + = 1
Multiply by 90g to clear the denominators, cancel and you have:
2g(12) + 3g(12) + 90(7) = 90g
24g + 36g + 630 = 90g
630 = 90g - 60g
630 = 30g
g = 630/30
g = 21 minutes, GG working alone
:
:
;
See if that checks out using a calc
12/45 + 12/30 + 7/21 =
.267 + .400 + .333 = 1, confirms our solution of 21 minutes

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