There is a "secret" accounting method in the kingdom of mathematics. When they earn 300 yuan, it is recorded as - 240 yuan; when they spend 200 yuan, it is recorded as + 260 yuan June 8 expenditure 100 yuan, 20 account - 1200 yuan ① How much should be recorded in the account on June 8? Please explain the reason ② What is the actual revenue and expenditure on June 20?
Let the algebraic formula between revenue and bookkeeping be y = ax + B, substitute x = 300, y = - 240, get - 240 = 300A + B, substitute x = - 200, y = 260, get 260 = - 200A + B, solve the equations, get a = - 1, B = 60. The algebraic formula of secret bookkeeping is y = - x + 60
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