If 3a+5b=10 and 5a + 3b=30, what is the average (arithmetic mean) of a and b?

If 3a+5b=10 and 5a + 3b=30, what is the average (arithmetic mean) of a and b?

A 4

B 2.5

C 2.5

D 4.5

Solution

Correct Answer: Option B

3a+5b=10 ..................... (1)

5a + 3b=30 ....................... (2)

We get from (1) + (2),

8a + 8b = 40

or, a + b = 5 (Dividing both sides by 8)

Now, The average would be,

(a + b)/2 = (5)/2 = 2.5