Question

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

Answer 1

The Correct Option is B

Step 1: Define variables. 

Let the number of red balls be \( r \), blue balls be \( b \), and green balls be \( g = 7 \).

Step 2: Set up the total number of balls equation.

\[ r + b + g = 20 \]

Substituting \( g = 7 \):

\[ r + b + 7 = 20 \]

Simplifying:

\[ r + b = 13 \]

Step 3: Apply the condition on red and green balls.

We are given that the sum of red and green balls is less than 13:

\[ r + 7 < 13 \]

Simplifying:

\[ r < 6 \]

Thus, the maximum number of red balls is 5.