*After Fitrah spent 20% and Sophia spent 30% of her monthly salary,both had the same amount of money left.If Fitrah's monthly salary RM1800 how much was Sophia's monthly salary? *

Let Fitrah's monthly salary be F. (and F = RM 1800)

Let Sophia's monthly salary be S.

They are both left with the same amount. Call this amount X. Then,

(1 - 20%)*F = X (Fitrah spent 20% and was left with X)

(1 - 30%)*S = X (Sophia spent 30% and was left with X)

Simplifying these eqns,

0.8*F = X

0.7*S = X (now substitute for F = 1800)

0.8*1800 = X

0.7S = X

From 0.8*1800 = X, then X = 1440

From 0.7S = X = 1440, then S = 1440/0.7 = 2057.14

Sophia's monthly salary is: RM 2057.14