Answer: Option B
:
B
Using the conventional approach :
Saif takes 10 hrs.
So total time they both would take without talking $=\frac{10\times 9}{19}=\frac{90}{19}$ hrs.
But they take 5 hrs $=\frac{95}{19}$ hrs.
So time wasted is $\frac{5}{19}$ hrs.
They work for 5 hrs and put 10 bricks less per hour, so they had to put in extra time for $5\times 10=50$ bricks.
Now, extra time taken=$\frac{5}{19}$ hrs.
so, in $\frac{5}{19}$ hrs: 50 bricks
5 hrs: x
x=950 bricks.
But this includes the 50 bricks extra put in the time $\frac{5}{19}$ hrs. So total number of bricks is 900.
Using percentage approach:
Aamir takes 9 hours,$\Rightarrow$ he does $11.11\%$ of the work every hour
Saif takes 10 hours $\Rightarrow$ he does 10% of the work every hour
Together they finish $21.11\%$ of the work
Given that they take 5 hours to finish the work after chatting, which means they are actually finishing $\frac{100}{5}=20\%$ of the work
The remaining $1.1\%$ accounts for the 10 bricks decrease due to chatting
Thus, $100\%$ corresponds to 900. Answer is option (b)