Question

Two cargo trains are linked together, making of a total of 22 cars. The cars from one of the trains are carrying 15 tons each, and those from the other train are carrying 20 tons each. If the total cargo weight ranges from 380 to 400 tons, what is the range of the number of 20 tons cars? (Fill in the equation)
Let x be the number of 20 tons cars.

380 < 15 ( ) + 20 < 400

Answer 1

Let x be the number of 20 ton cars

Then,
380<{15(22-x)+20x}<400
380<{330-15x+20x}<400
380<{330+5x}<400

Subtract 330 on both sides
50<5x<70

Divide both sides by 5;
10<x<14

Therefore, the range of 20 tonne cars is between 10 and 14 cars.