The ratio of sand to gravel in a mixture is 7 : 8 while that between gravel and cement is 6 : 7. What is the ratio of sand to cement in the mixture?

Consider the following question followed by the statements and decide which of the statements is sufficient to answer the question.
Question:
8 trolleys in a supermarket are used to load and unload commodities. All of the trolleys have been filled with oil cans of two different sizes and shapes. How many cans are loaded in the trolleys in total?
Statements:
1. The shape of 8 cans are such that in one trolley only 2 can fit.
2. The rest of the trolleys are filled with 4 oil cans each.

Find the figure that can replace the question mark in the following analogy.

Which of the numbers given below is NOT rational?

The standard deviation of the set {10, 11, 12, 9, 8} is