Let x be the initial amount of money. We know that mum spent 2/3 of this amount, so she's left with
[tex] x - \dfrac{2x}{3} = \dfrac{x}{3} [/tex]
Of this remainder, only 1/4 was deposited, which is
[tex] \dfrac{x}{3}\times \dfrac{1}{4} = \dfrac{x}{12} [/tex]
And this amount equals 20, so we have
[tex] \dfrac{x}{12} = 20 \iff x = 20\times 12 = 240 [/tex]
