Paul creates a CD by mixing together

songs that are either 3 minutes or

4 minutes long. His CD has 22 songs

and is 78 minutes long. How many

three-minute and how many four-minute

songs did he use?

Paul created 10 three minutes songs and 12 four minutes songs.

Step-by-step explanation:

The song he created on his CD is either 3 minutes long or 4 minutes long.

His CD has 22 songs and is 78 minutes. The number of 3 minutes and 4 minutes song can be calculated below.

Let

a = number of 3 minutes song

b = number of 4 minutes song

number of song = 22

a + b = 22 ... (i)

3a + 4b = 78 ... (ii)

Make a subject of the formula in equation (i)

a = 22 - b

Insert the value of a in equation (ii)

3 (22 - b) + 4b = 78

66 - 3b + 4b = 78

b = 78 - 66

b = 12

insert the value of b in equation (i)

a + b = 22

a + 12 = 22

a = 22 - 12

a = 10

Paul created 10 three minutes songs and 12 four minutes songs.