Answer: 50 pairs.
Explanation:
For each pair of earrings, Joshua spends $0.29 + $0.11 in materials.
So he spends $0.40 for each pair of earrings.
If he has $20, we want to know how many times he can spend $0.40.
For this, we take the quotient:
$20/$0.40 = 50
This means that we can sperate $20 into 50 times $0.40.
So he can buy enough material to make 50 pairs of earrings.