Answer: The largest value of 'a' is less than 20
Explanation:
If arithmetic mean of 3a and 4b is less than 50 i.e 3a+4b/2 < 50
3a+4b < 100... (1)
If a is twice as b, a = 2b... (2)
Substituting equation 2 into 1 we have, 3(2b)+4b < 100
6b+4b < 100
10b < 100
b < 10
Since a = 2b, a = 2×10 = 20
Therefore the largest value of 'a' is less than 20 which can be 19.9