Answer: The number of red tiles = 15.
Step-by-step explanation:
Let the number of red tiles be x, and the total tiles be y.
Since, the pattern he used equal numbers of red white tiles, therefore the number of white tiles = x
The number of blue tiles = 20
Forty percent of the pattern was made of blue tiles and 40%=0.40
Therefore,
[tex]0.40y=20\\\Rightarrow\ y=\frac{20}{0.4}\\\Rightarrow\ y=50[/tex]
Now, the total number of tiles = [tex]x+x+20=50[/tex]
[tex]\Rightarrow\ 2x=50-20\\\Rigjhtarrow\ x=30\\\Rightarrow\ x=15[/tex]
The number of red tiles = 15.