the box contains cereal. Only 3/4 of the box has cereal remaining.
From the remaining cereal fraction, 2/5th is consumed.
then the portion of cereal consumed is
[tex] \frac{2}{5} of \frac{3}{4} [/tex]
when the 'of' function is used it means the fractions should be multiplied
then numerators should be multiplied by numerators and denominators by denominators
[tex] \frac{2*3}{5*4} = \frac{6}{20} [/tex]
this can be further simplified by dividing both numerator and denominator by a factor common to both , in this case both 6 and 20 are divisible by 2
[tex] \frac{6}{20} / 2 = \frac{3}{10} [/tex]
answer is 3/10th of the box is consumed