What is the "row heading" of the third row (marked with the question mark) in the table shown below?

**4** : 6, 11, 7
**3** : 8, 4, 12
**?** : 10, 55, 15

Explain the scheme used.

We observe that:

(6+11+7) = 24 = 6*4

(8 + 4 + 12)= 24 = 8*3

Hence, the sum of the second, third and fourth numbers in a row

= product of the first and the second numbers

Let the missing number be x.

Then,

10x = 10 + 55+ 15 = 80, so that x = 8

Hence the required number is 8.

*Edited on ***February 6, 2009, 3:28 pm**