Mixtures and alligation

Example 1 · level 1

In what ratio must a grocer in Nagpur mix basmati rice costing ₹40/kg with basmati rice costing ₹65/kg so that the mixture costs ₹47/kg?

1. 19 : 7
2. 7 : 18
3. 18 : 7
4. 8 : 13

Example 2 · level 2

In what ratio must a grocer in Kochi mix dal costing ₹70/kg with dal costing ₹80/kg so that the mixture costs ₹77/kg?

1. 3 : 7
2. 7 : 8
3. 7 : 3
4. 4 : 7

Example 3 · level 3

A container has 40 litres of milk at a dairy in Anand. 4 litres are taken out and replaced with water. This is done 3 times in all. How many litres of milk are left?