Alligation or Mixture - General Aptitude

Q1:

In what ratio must a grocer mix two varieties of pulses costing Rs. 15 and Rs. 20 per kg respectively so as to get a mixture worth Rs. 16.50 kg?

A 3 : 7

B 5 : 7

C 7 : 3

D 7 : 5

ANS:C - 7 : 3

By the rule of alligation:

Cost of 1 kg pulses of 1st kind Cost of 1 kg pulses of 2nd kind
Rs. 15 Mean Price
Rs. 16.50
Rs. 20
3.50 1.50
Required rate = 3.50 : 1.50 = 7 : 3.