A real-life situation gives a linear function. Write the function, name its type and use it to find the values asked for.

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Write what is given and what is to be found. Note the fixed part, the rate, and what x stands for.
2 · Write the function from the situation. Fixed part + rate × quantity, e.g. f(x) = 15x + 40, where x is the distance in km.
3 · Name the type. It has the form mx + c with m ≠ 0, so it is a linear function.
4 · Find the value asked for. Substitute: f(12) = 15 × 12 + 40 = 220.
5 · Work backwards when the output is given. Solve 15x + 40 = 340 to get x = 20.
6 · Check and box the answer. Substitute back, and write the units: ₹ 220, 20 km.

Scoring tip: Always say what x stands for, and write units (₹, km, litres) in the final answer.