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23. We have a 630 ml mixture of milk and water in the ratio 7:2. How much water must be added to make the ratio 7:3? | |

A. 60 ml | B. 70 ml |

C. 50 ml | D. 80 ml |

Answer: Option B

Explanation:

concentration of water in mixture1 $=\dfrac{2}{9}$ *(since the ratio of milk and water = 7:2)* ...(1)

concentration of water in pure water= 1 ...(2)

Now the above mentioned items are mixed to form mixture2 where milk and water ratio = 7 : 3

=> concentration of water in mixture2 $=\dfrac{3}{10}$

By rule of alligation,

concentration of water in mixture1 $\left(\dfrac{2}{9}\right)$ | concentration of water in pure water (1) | |||||||||

Mean concentration | ||||||||||

$\left(\dfrac{3}{10}\right)$ | ||||||||||

$1-\dfrac{3}{10}=\dfrac{7}{10}$ | $\dfrac{3}{10}-\dfrac{2}{9}=\dfrac{7}{90}$ |

=> Quantity of mixture1 : Quantity of water

$=\dfrac{7}{10}:\dfrac{7}{90}=\dfrac{1}{10}:\dfrac{1}{90}=1:\dfrac{1}{9}$

Given that Quantity of mixture1 = 630 ml

=> 630 : Quantity of water $=1:\dfrac{1}{9}$

=> Quantity of water $=630 ×\dfrac{1}{9}=70$ ml

M.Suresh

2016-08-25 09:30:13

Let water + milk = 630 ml

from the question M:W=7:2. So,

water quantity = 2/9 * 630 = 140

milk quantity =630-140=490,

then,

490/(140+x)=7/3

=> 1470-980=7x

=> x=490/7 = 70

from the question M:W=7:2. So,

water quantity = 2/9 * 630 = 140

milk quantity =630-140=490,

then,

490/(140+x)=7/3

=> 1470-980=7x

=> x=490/7 = 70

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