A box contains 80 paper clips, some of which are grey, some are yellow and the rest are blue. The probability of drawing a grey clip is $1/5$ and the probability of drawing a yellow clip is $1/4$.

1. Find the number of grey and yellow clips, then subtract from the total.

Number of grey clips $= \dfrac{1}{5}\times 80=16$

Number of yellow clips $= \dfrac{1}{4}\times 80=20$

Number of blue clips $=80-16-20=44$

1. Express the new number of blue clips and total clips after removing $x$ blue clips.

From part (a), the original number of blue clips is $44$.

After removing $x$ blue clips,

number of blue clips $=44-x$,

total number of clips $=80-x$.

2. Set up and solve the probability equation.

$\frac{44-x}{80-x}=\frac{7}{25}$

$25(44-x)=7(80-x)$

$1100-25x=560-7x$

$540=18x$

$x=30$