Question

The following rainfall data refers to station A and B which are equidistant from station X :

	Station A	Station X	Station B
Long - term normal annual rainfall in mm	200	250	300
Annual rainfall in mm for the year 1940	140	P	270

The value of P will be

• A. 250
• B. 220
• C. 205
• D. 200

Answer 1

The correct option is D 200

Since the normal annual rainfall at stations A and B does not lie within 10% of the normal annual rainfall at station X.
So, using normal ratio method, we get

$P=\frac{250}{2}[\frac{140}{200}+\frac{270}{300}]=200\text{mm}$

If the normal annual rainfall at non-missing station lie within 10% of that at missing station then arithmetic average method can be used.