Electricity consumption cost

Last year Carol's family reduced its electricity consumption by 31% compared to the previous year and paid CZK 2883 less. How much CZK was electricity last year, and how many two years ago?

Correct answer:

a =  6417
b =  9300

Step-by-step explanation:


a = b - 31/100 b
a = b - 2883

a = b - 31/100·b
a = b - 2883

100a-69b = 0
a-b = -2883

Row 2 - 1/100 · Row 1 → Row 2
100a-69b = 0
-0.31b = -2883


b = -2883/-0.31 = 9300
a = 0+69b/100 = 0+69 · 9300/100 = 6417

a = 6417
b = 9300

Our linear equations calculator calculates it.



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