Let Alka’s monthly income be Rs x.
Alka spends 90% of the money that she receives every month.
∴ Amount spent by Alka = 90% of x
= (90/100) × x = 0.9x 100
Now, Savings = Income – Expenditure
∴ 120 = x – 0.9x
∴120 = 0.1 x
∴ x = 1200
Alka gets Rs 1200 monthly.