There are 20 balls which are red, blue or green. If 7 balls are green and the…
2026
There are 20 balls which are red, blue or green. If 7 balls are green and the sum of red balls and green balls is less than 13, at most how many red balls are there?
- A.
4
- B.
5
- C.
6
- D.
7
Attempted by 437 students.
Show answer & explanation
Correct answer: B
Answer: 5
Let r, g, b be the numbers of red, green, and blue balls.
Given g = 7.
From r + g < 13 we get r + 7 < 13, so r < 6.
r must be a whole number, so the largest possible integer less than 6 is 5.
Check feasibility: if r = 5 and g = 7, then b = 20 - 5 - 7 = 8 ≥ 0, so this is valid.