Question

A digital camera memory card is 1/4 full. The card is 2/3 full when 375 more pictures have been taken.

Answer 1

Let

x--------> total of images that the memory card can contain

we know that

$\frac{2}{3} x=\frac{1}{4} x+375$

Multiply by $12$ both sides

$8x=3x+375*12\\ 8x-3x=4,500\\ 5x=4,500\\ x=900 pictures$

originally on the memory card

$\frac{1}{4} x\\ =\frac{1}{4} *900\\ =225 pictures$

therefore

the answer part a) is

$900 pictures$

the answer part b) is

$225 pictures$

Answer 2

To get the answer first we have to find full numbers.
We can use proportion
2/3 ----------------------- 375
1 -------------------------- x
Crossmultiply now
2/3*x=375           /:2/3 
x=$375: \frac{2}{3}$ 
x=$375* \frac{3}{2}=562$ - its the answer A)
Now we have to find how much were originally on the card.
To get the answer we can just multiply 562 times 1/4.
562*1/4=140 - its the asnwer B)