Question

a and b can point a house in 28 days withe the help of c they can paint in 21 days how long would c take by himself​

Answer 1

ANSWER:

A can do a work in = 20 days

Let B can do the work in =X days

Both A and B can do the work in = 1/12 days

Therefore 1/20 + 1/X= 1/12

So 12 (X+20) = 20 X;

So 8X= 240 ; X= 30.

Therefore “B” can do the work alone in 30 - days.

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Another Simple Method:

In 12- days A- can complete= 12/20= 3/5- part of the work.

So in 12- days B- can complete (1–3/5) = 2/5- part of the work.

So complete work can be done by B- alone in 12÷ (2/5)= 12 x5/2= 30- days.

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HOPE IT IS HELPFULL

Answer 2

Step-by-step explanation:

A & B together can complete work in (25x20)/(25+20) =500/45 = 100/9 days.

They complete 5 x 9/100= 9/20 work in 5 days.

Remaining 11/20 work done by B in 11/20 x 20 = 11 days.

Method 2

A works only for 5 days completing 5/25 = 1/5 part of work.

Remaining 4/5 work is done by B in 4/5 x 20 = 16 days.

=> B works for 11 days after A leaves.

Method 3

Let B take m days after A leaves.

Since A & B work together for 5 days, we have :

5/25 + (5 + m)/20 = 1

Taking LCM as 100,

20+ 5(5 + m) = 100

=> 20 + 25 + 5m = 100

5m = 100 - 45 = 55

m = 55/5= 11 days.

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