LaToya had a large collection of basketball cards. She decided to give half of them to her friend, Erin, and a fourth of them to her brother. She still has 150 cards left. How many cards did she start with?

If you don't think you can write a formula, it's still pretty easy to figure out.
Draw some boxes on paper, a long one for 1/2 the cards, and a short one for 1/4. What's left, to make 1/2 and 1/4 = 1? Another 1/4, right? So draw that last small box.

So what KNOWN number will you put in the last box?
And if you know that one, what's the middle one?
And if half is twice 1/4, what number in the big box?
Now add them all up.