Hello, nimanamjouyan!

A rice company decides to combine a first-rate rice that costs 5000 per kg

with a second-rate type costs 4000 per kg.

The result is a mixture of rice which costs 4600 per kg.

How many kilograms of the first rate rice are there in 40 kg of the mixture?

. .

Let = kg of first-rate rice.

Then = kg of second-rate rice.

We have kg of first-rate rice at 5000/kg.

. . Its value is: .

We have kg of second-rate rice at 4000/kg.

. . Its value is: .

The total value of the mixture is:

. . .[1]

But we know that mixture will be 40 kg of rice at 4600/kg.

. . Its value will be: . .[2]

We just described the value of the mixture intwoways.

There is our equation! .