Question

6. In a certain year, the consumption pattern of electricity charges in a town:
• Cost of first 30 units = $1.00/unit
• Cost of next 30 units = $7.00/unit
• Cost of each additional unit = $5.00
(a) If Amaka used 420 units in January, calculate the amount paid.
(b) If Amaka paid $2,740.00 in February, calculate the number of units consumed.
(c) Find, correct to two decimal places, the percentage change in units of electricity consumed by Amaka in January and February.

Accepted Answer

(a) Cost = 30×$1 + 30×$7 + 360×$5
   = $30 + $210 + $1,800 = $2,040.00
(b) Remaining after first 60 units cost:
   $2,740 − $30 − $210 = $2,500
   Units = 2500/5 = 500
   Total = 500 + 30 + 30 = 560 units
(c) Change = 560 − 420 = 140 units
   % change = (140/420) × 100 = 33.33%

WAEC Mathematics 2025 Theory — Question 6

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