Question

this question of class 8.....

Answer 1

hey!

Let a complete work be as 1.

A complete work in 25 days,

So in 1 day, A do work = 1/25

B complete work in 20 days,

So in 1 day, B do work = 1/20

In 5 days both do work = 5*(1/25)+5*(1/20) = 1/5+1/4 = 9/20

So 9/20 work is completed in 5 days.

Now, remaining work=1–9/20 = 11/20

So B will complete work in = (11/20)/(1/20)=11 days

Answer 2

X can complete the remaining work in 13 3/4 days

Given:

X can do a piece of work in 25 days

Y can do a piece of work in 20 days

X and Y worked together for 5 days

After that Y leaved the work

To find:

In how many days X will complete the remaining work

Solution:

Given X can do a piece of work in 25 days  

⇒ The work can be done by X in 1 day = 1/25

Y can do a piece of work in 20 days  

⇒ The work can be done by Y in 1 day = 1/20  

From above data,

The work can be done by X and Y together in 1 day = $\frac{1}{25} + \frac{1}{20} = \frac{9}{100}$  

Given that X and Y worked for 5 days

The work can be completed in 5 days =  $5(\frac{9}{100} )$ = $\frac{9}{20}$

Remaining work will be =  $1 -\frac{9}{20}$  =  $\frac{11}{20}$  

As we know X can do 1/25 of work in 1 day  

Then number days to complete $\frac{11}{20}$ of work

= Remaining work / work done in 1 day = $\frac{(11/20)}{(1/25)}$   = $25 (\frac{11}{20} )$

= 55/4 = 13 3/4 days

X can complete the remaining work in 13 3/4 days

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