Question

how many kilos of tea worth rs 72 per kg should be mixed with 10 kg of tea worth rs 90 per kg to produce a mixture which will cost rs 78 per kg

Answer 1

Price. Quantity
Tea type I 90 ----------------10 kg
Tea type II 72 ----------------x kg
Mixture 78 ---------------- 10+x kg

sum of individual components = quantity in mixture
90*10+72x=78(10 +x)
900+72x =780+78 x
72x -78 x=-120
-6x=-120
x= -120 / -6
x= 20
20 kg of Tea type II costing Rs. 72 has to be added