IMPORTANT
FACTS AND FORMULAE
1
.
Alligation
: It is the rule that enables us to find the ratio in which two or more ingredients at
the given price must be mixed to produce a mixture of a desired price.
2
.
Mean Price
: The cost price of a unit quantity of the mixture is called the mean price.
3.
Rule of Alligation
: If two ingredients are mixed, then
(Quantity of cheaper)
= (C.P. of dearer)  (Mean price)
(Quantity of dearer)
(Mean price)  (C.P. of cheaper)
We present as under:
C.P. of a unit quantity of cheaper
C.P. of a unit quantity of dearer
(c)
(d)
(m)
(dm)
(mc)
∴
(Cheaper quantity) : (Dearer quantity) = (d  m) : (m 
c).
4. Suppose a container contains x units of liquid from which y units are taken out and replaced
by water. After n operations the quantity of pure liquid
=
[
x(1y/x)^n
]
units.
.
SOLVED EXAMPLES
Ex. 1. In what ratio must rice at Rs. 9.30 per kg be mixed with rice at Rs. 10.80 per kg so that
the mixture be worth Rs. 10 per kg ?
Sol
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 Spring '11
 vinh
 Kilogram, Litre, Rs., C.P., Sol. C.P.

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