On a certain assembly line the rejection rate for hyundai i10's production was 4 percent for hyundai i20's production 8 percent and the two cars combined 7 percent. What was the ratio of hyundai i20's production to hyundai i10's production?

Correct option is D

Given
Rejection rate for i10 = 4%
Rejection rate for i20 = 8%
Combined rejection rate = 7%

Formula Used
Rule of Alligation:
Quantity ratio of A to B = $$(\text{Rate of B} - \text{Mean Rate}) : (\text{Mean Rate} - \text{Rate of A})$$​​
Solution
Using the alligation method for i10 and i20:
Difference between i20 rate and combined rate = 8 - 7 = 1 (This corresponds to i10's ratio part)
Difference between combined rate and i10 rate = 7 - 4 = 3 (This corresponds to i20's ratio part)
So, the ratio of production of i10 to i20 is 1:3.
The question asks for the ratio of i20's production to i10's production.
Therefore, the ratio is 3:1.

Final Answer
So the correct answer is (d)