Adigital camera memory card is 1/4 full. the card is 2/3 full when 375 more pictures have been taken.
a) how many pictures can the memory card hold? ?
b) how many pictures were originally on the memory card? ?

Let the number of pictures the card holds = X
The card is already full by 1/4 = X/4
when 375 more pictures are taken then card is full by 2/3
Then
X/4+375= 2X/3
(2X/3)-(X/4)=375
(8X/12)-(3X/12)=375
5X/12=375
X=(375*12)/5
X= 900
So the total number of pictures memory card can hold = 900
Number of pictures originally on the memory card = X/4
                                                                                 = 900/4
                                                                                 = 225

Sis less than or equal to 75 (bottom left)

Main idea on left, details on right