If a : b = c : d, then $\dfrac{ma + nc}{mb + nd}$ is equal to :

1. m : n

2. dm : cn

3. an : mb

4. a : b

In an alloy, the ratio of copper and zinc is 5 : 2. If 1.250 kg of zinc is mixed in 17 kg 500 g of alloy, then the ratio of copper and zinc in the alloy will be :

1. 1 : 2

2. 2 : 1

3. 2 : 3

4. 3 : 2

If a sum of ₹ x is divided between A and B in the ratio $\dfrac{a}{b} : \dfrac{c}{d}$, then A gets:

1. ₹$\Big(\dfrac{abx}{ac + bd}\Big)$

2. ₹$\Big(\dfrac{abx}{ad + bc}\Big)$

3. ₹$\Big(\dfrac{adx}{ad + bc}\Big)$

4. ₹$\Big(\dfrac{adx}{ab + cd}\Big)$

The ratio of the number of boys and girls in a school of 720 students is 7 : 5. How many more girls should be admitted to make the ratio 1 : 1?

1. 90

2. 120

3. 220

4. 240