0.9 of Karen's Science score is equal to 0.75 of her Math score and 0.8 of her Chemistry score. Given that Karen scored 96 marks for her Math, what was her total score of the 3 subjects?

You have to formulate equations for this problem.

Let S = Science score

M = Math score

C = Chemistry score

To illustrate the given:

0.9S = 0.75M

0.9S = 0.8C

You are given that Karen’s Math score is 96 marks. You have to substitute the Math score to the first equation.

0.9S = 0.75 (96)

0.9S = 72

S = 80

Therefore, Karen’s Science score is 80. Now, you have to substitute the Science score to the second equation.

0.9 (80) = 0.8C

0.8C = 72

C = 90

So, Karen’s Chemistry score is 90.

Therefore, the total score of the 3 subjects is 266 (96 + 80 + 90).