Answer:
1/5 or 20%
Explanation:
The total number of paintings is 60.
60 = x (x − 2) + x + 2x + 8 + 10
60 = x² − 2x + x + 2x + 18
0 = x² + x − 42
0 = (x + 7) (x − 6)
x = -7 or 6
Since x can't be negative, x = 6. So the number of paintings from the 20th century is 6 (6 − 2) + 6 = 30.
The number of paintings that are both British and from the 20th century is 6.
So the probability that a painting from the 20th century is also British is 6/30 = 1/5, or 20%.