Alka spends 90% of the money that she receives every month, and saves Rs. 120. How much money does she get monthly?

Hint: The percentage of monthly expenditure from Alka’s salary is 90%. We know that the summation of the percentage of expenditure and saving is 100%. Now, get the percentage of the monthly saving. Assume the money that Alka receives in a month is Rs. x. The monthly saving is (10% of x). It is given that the monthly saving of Alka is Rs. 120. Now, solve it further and get the value of x.

Complete step-by-step answer:
According to the question, it is given that Alka spends 90% of the money that she receives every month, and saves Rs. 120. We have to find a monthly salary for Alka.
The percentage of monthly expenditure from Alka’s salary = 90% ……………………………(1)
We know that the summation of the percentage of expenditure and saving is 100%. So, to get the percentage of monthly savings from Alka’s salary, we have to deduct the expenditure percentage from 100%.
The percentage of monthly saving from Alka’s salary = 100%-10% …………………………………(2)
The monthly saving of Alka = Rs. 120 …………………………..(3)
Now, let us assume that Alka receives Rs. x monthly.
Since Alka saves 10% of her saving from her salary and her salary is Rs. x. So, the saving of Alka is equal to (10% of x).
The monthly saving of Alka = Rs. (10% of x) = Rs. \[\dfrac{10}{100}\times x\] = Rs. \[\dfrac{x}{10}\] …………………………………(4)
From equation (3) and equation (4), we have the monthly saving of Alka.
Now, on comparing equation (3) and equation (4), we get
\[\begin{align}
  & \Rightarrow \dfrac{x}{10}=120 \\
 & \Rightarrow x=120\times 10 \\
 & \Rightarrow x=1200 \\
\end{align}\]
We have got the value of x equal to Rs. 1200.
Hence, the money that Alka receives is Rs. 1200.

Note: In this question, one might take 90% as the saving and make it equal to Rs. 120. This is wrong because the percentage of the expenditure of Alka’s salary is 90%. So, cannot take 90% as a percentage of the savings. To get the percentage of the savings we have to deduct the percentage of the expenditure from 100%.