Solve the Fraction Addition: 4/8 + 4/10

List the multiples of each number: 8: 8, 16, 24, 32, 40... and 10: 10, 20, 30, 40... The first number that appears in both lists is 40, so that's your LCD!

Because fractions represent parts of different wholes! $\frac{4}{8}$ means 4 parts of something divided into 8 pieces, while $\frac{4}{10}$ means 4 parts of something divided into 10 pieces. You need equal-sized pieces first!

For $\frac{4}{8}$: since 8 × 5 = 40, multiply by $\frac{5}{5}$
For $\frac{4}{10}$: since 10 × 4 = 40, multiply by $\frac{4}{4}$

Yes! $\frac{36}{40}$ can be simplified by dividing both numerator and denominator by their GCD, which is 4. So $\frac{36}{40} = \frac{9}{10}$.

You could first simplify $\frac{4}{8}$ to $\frac{1}{2}$, then find LCD of 2 and 10 (which is 10). This gives $\frac{5}{10} + \frac{4}{10} = \frac{9}{10}$!