From the given table the values of a, b and c are :

C.I.	Frequency	Cumulative Frequency
30-40	24	24
40-50	a	40
50-60	12	b
60-70	c	60

1. a = 16, b = 52 and c = 8

2. a = 16, b = 12 and c = 8

3. a = 40, b = 52 and c = 60

4. a = 40, b = 12 and c = 60

From table,

⇒ 24 + a = 40

⇒ a = 40 - 24 = 16

⇒ b = 40 + 12 = 52

⇒ b + c = 60

⇒ 52 + c = 60

⇒ c = 60 - 52 = 8.

Hence, Option 1 is the correct option.