有一天，一个女孩参加数学考试只得了38分。她心里对父亲的惩罚充满恐惧，于是偷偷把分数改成了 88分。...

The key to solving this riddle lies in understanding the significance of the '8' being "half green and half red," and the implications it has for the father and daughter.

Here's the breakdown:

1. The Girl's Attempt to Change Her Score:

   • The girl scored 38 on her math exam.
   • Fearful of her father's reaction, she tried to change it to 88 by altering the '3' to an '8'.
   • She used pens available to her, which happened to be green and red.

2. Father's Observation:

   • Upon seeing the altered score, the father noticed that the '8' was "half green and half red."
   • He interpreted this as a clumsy attempt to deceive him.
   • He reacted angrily, thinking his daughter was trying to fool him.

3. The Underlying Issue:

   • The girl didn't realize she used two different colors because she is red-green color-blind.
   • Red-green color blindness is extremely rare in females because it is an X-linked recessive trait.
   • For a female to be red-green color-blind, she must inherit the mutated gene from both parents:
     • Her father must be color-blind.
     • Her mother must be at least a carrier of the gene.

4. Father's Realization and Breakdown:

   • After the confrontation, the father reflects on the situation.
   • He realizes that his daughter didn't intentionally use two colors; she couldn't distinguish between red and green.
   • This means she is red-green color-blind.
   • Since he is not color-blind, he understands that he cannot be her biological father.
   • This revelation leads to his emotional breakdown.

Answer:

Because he realized his daughter is red-green color-blind—which is rare in females and suggests he isn’t her biological father—so he broke down upon understanding this.