Using the table, what is the value of f₁ + f₂?

Correct answer: c 18

The modal class is 60−64 (20); f₁ = 20 − 10 = 10, f₂ = 20 − 12 = 8; the sum is 18.

Why the other options are wrong

• a 10: 10 is f₁ alone; f₁ + f₂ also needs f₂ = 8 added, so the sum is larger than this.
• b 12: 12 is the frequency of 65−69; f₁ + f₂ is different.
• d 20: 20 is the modal class's own frequency, not f₁ or f₂; those come from subtracting the frequencies of the classes before and after it.