It doesnt even makes sense

His answer is correct.

Oh really? The digit looks....

The digits are merely recurring decimals.

The values can also be expressed as fractions.

Paint A : 6 units
Paint B : 5 units
Total : 11 units

Fraction of the paint mixture that is made of Paint A
= 6/11

Fraction of the paint mixture that is made of Paint B
= 5/11

Mass of paint in 50kg mixture that is made of paint A

= 6/11 x 50 kg
= 27 3/11 kg

Mass of paint in 50kg mixture that is made of paint B

= 50 kg - 27 3/11 kg
= 22 8/11 kg

Cost of Paint A

= 27 3/11 kg x $2.50/kg

= $ 68 2/11 (or $68.1818181818181....)


Cost of Paint B

= 22 8/11 kg x $1.40/kg

= $ 31 9/11 (or $31.818181818181....)


Total cost

= $ 68 2/11 + $ 31 9/11

= $100

Okok thanks

For every 6 kg of A and 5 kg of B, total cost = 6 x 2.50 + 5 x 1.40
= $22

So, 11 kg of the mixture costs $22.

In a proper mixing and maintaining the same ratio,

1 kg of the mixture costs $2.
So, 50 kg of the mixture costs $100.

This method would be less confusing since it avoids fractions altogether. But the student must be able to visualise the obtainment of 11kg