O-Level Additional Math

[Daddy]

Hi,

Need someon help on this sec 1 question. Thanks

3 workers, Alpha, Beta and Charlie take 6 hrs, 7 hrs and 9 hrs respectively to paint a hall alone. All 3 of them decided to work together to complete the painting of the hall. After 2 hrs, Alpha and Beta left away. How long does it take for Charlie to complete the painting?

Thanks you…

[dazzlego]

Daddy:

Hi,

Need someon help on this sec 1 question. Thanks

3 workers, Alpha, Beta and Charlie take 6 hrs, 7 hrs and 9 hrs respectively to paint a hall alone. All 3 of them decided to work together to complete the painting of the hall. After 2 hrs, Alpha and Beta left away. How long does it take for Charlie to complete the painting?

Thanks you...

Hi Daddy,

A can do 1/6 of the work in 1 hour
B can do 1/7 of the work in 1 hour
C can do 1/9 of the work in 1 hour
A,B,C can do 1/6 + 1/7 + 1/9 = 53/126 of the work in 1 hour
In 2 hours, A,B,C can do 106/126 of the work
Thus, C need to do 20/126 = 10/63 of the work by himself
10/63 ÷ 1/9 = 10/7 hours

Cheers :celebrate:

[Daddy]

Thanks dazzlego,


I still not very clear on the hightlight

In 2 hours, A,B,C can do 106/126 of the work
Thus, C need to do 20/126 = 10/63 of the work by himself
10/63 ÷ 1/9 = 10/7 hours

Can I write the answer 1.43hrs instead of 10/7hrs?

Thanks.

[Jtutor]

If I may add:

C needs to do (1-106/126) = 20/126 of the work which is remaining.
1/9 -> 1 hr
20/126 or 10/63 -> (10/63)/(1/9) * 1 hr = 10/7 hrs
Your answer can also be 1 3/7 hrs or 1.43 hrs (3sf)
Cheers!

[Daddy]

Thank Jtutor.

[Daddy]

Thank Jtutor.

[Daddy]

Thank Jtutor.

[Daddy]

Thank Jtutor.

[Daddy]

Thank Jtutor.

[Jtutor]

You are welcome!