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Linear functions and straight-line graphs sheet
Structured-answer frame

A printing shop's cost is Rs. 16,000 for 100 cards and Rs. 22,000 for 250 cards. Find the linear cost function, explain the slope and intercept, and find the cost of 400 cards.

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

  1. 1 · Write the two points. (100, 16,000) and (250, 22,000).
  2. 2 · Find the slope. m = 6,000 ÷ 150 = 40.
  3. 3 · Use point-slope form. C − 16,000 = 40(x − 100), so C = 40x + 12,000.
  4. 4 · Interpret. Slope: Rs. 40 variable cost per card. Intercept: Rs. 12,000 fixed cost.
  5. 5 · Sketch and use the line. [Sketch: line starting at 12,000 on the C-axis, rising 40 per card]
  6. 6 · Predict. C(400) = 16,000 + 12,000 = Rs. 28,000.