Only matching slices can be counted
Before you read anything
Three eighths of a bar, and two eighths more. Say the answer out loud before you write anything.
Now say what the bottom number of your answer is, and why it is not sixteen.
Five of one thing
Five eighths. Nothing was added to the bottom because nothing happened to the pieces: they were eighths before and they are eighths after.
Adding fractions is counting
:x nutshell-like-slices
Pieces of the same size. Only like slices can be counted together — three sheep and two sheep are five sheep, and three sheep and two goats are not five of anything.
Three eighths is three of the things called eighths. Add two more of them and you have five of them. That is all the addition is, as long as they are :like slices.
Taking away is the same
$\frac{7}{9} - \frac{4}{9}$. Seven of them take four of them is three of them. The pieces never change size in either direction.
added the bottoms and got $\frac{5}{16}$
Musa made his answer smaller than what he started with. Sixteenths are half the size of eighths, so five of them is less than three eighths — and an answer smaller than one of the things you added is not an answer.
Check yourself
Six to try
$\frac{1}{5} + \frac{2}{5} = \frac{\square}{5}$. What goes in the box?
$\frac{4}{5} - \frac{3}{5} = \frac{\square}{5}$. What goes in the box?
$\frac{2}{6} + \frac{3}{6} = \frac{\square}{6}$. What goes in the box?
$\frac{4}{6} - \frac{1}{6} = \frac{\square}{6}$. What goes in the box?
$\frac{3}{8} + \frac{3}{8} = \frac{\square}{8}$. What goes in the box?
$\frac{5}{6} - \frac{3}{6} = \frac{\square}{6}$. What goes in the box?
Show that you have it
Adding, and taking away
$\frac{3}{5} + \frac{1}{5} = \frac{\square}{5}$. What goes in the box?
Zawadi drinks $\frac{3}{6}$ of a bottle in the morning and $\frac{2}{6}$ in the afternoon. How many $6$ths is that altogether?