Question

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

Answer 1

Tea type I 90 ----------------10 pounds
Tea type II 72 ----------------x pounds
Mixture 78 ---------------- 10+x pounds

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 pounds of Tea type II costing Rs. 72 has to be added 

Answer 2

here is your Answer
Tea1=20Kg...See Image For Answer