Hevesh wants to make 2 lines of dominoes that are both 21 inches long. Each line has dominoes spaced 1 and 1/2 inches apart. How many dominoes will she need for both lines?

Answer: 30 dominoes in total.

Step-by-step explanation:

Each line is 21 inches long.

the space between dominoes is 1 + 1/2 inches.

(assuming that the distance includes the domino itself) Now, we need at least two dominoes to see this distance,

The we have N + 1 dominoes per line, and the distance is:

N * (1 + 1/2) inches = 21 inches

If we find N, we can find the number of domineoes in each line:

N = 21 / (1 + 1/2) = 14

This means that we have 14 + 1 = 15 dominoes in each line, and we have two lines, so we have 30 dominoes in total.