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有幾題數學唔識做,,,,,,help

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1. Michael bought 24 stamps at a cost of $30. Some of the stamps are $1-stamps and the others are $2-stamps. How many $2-stamps did he buy?2. A cake is shared between Joseph and David. Joseph gets three quarters of the cake, and David gets the rest. If Joseph gives 100g of his share of cake to David, then Joseph... 顯示更多 1. Michael bought 24 stamps at a cost of $30. Some of the stamps are $1-stamps and the others are $2-stamps. How many $2-stamps did he buy? 2. A cake is shared between Joseph and David. Joseph gets three quarters of the cake, and David gets the rest. If Joseph gives 100g of his share of cake to David, then Joseph will have twice as much as David. Find the weight of the cake. 3. In a test consisting of 20 multiple-choice questions. 5 marks will be given for a correct answer, 3 marks will be deducted for a wrong answer and no marks for unanswered questions. If Simon answered 16 questions in the test and got 56 marks, how many questions did Simon answer correctly? 列步驟And式,thx!!!

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1. Michael bought 24 stamps at a cost of $30. Some of the stamps are $1-stamps and the others are $2-stamps. How many $2-stamps did he buy? Let Michael buy x $1-stamps, so he buy (24-x)$2-stamps x+2(24-x)=30 x+48-2x=30 -x+48=30 -x=-18 x=18 He buys 6 $2-stamps 2. A cake is shared between Joseph and David. Joseph gets three quarters of the cake, and David gets the rest. If Joseph gives 100g of his share of cake to David, then Joseph will have twice as much as David. Find the weight of the cake. Let the weight of cake be W and then Joseph gets (3/4)W David gets (1/4)W (3/4)W-100=2[(1/4)W+100] (3/4)W-100=(1/2)W+50 3W-400=2W+200 W=600 the weight of cake is 600g(唔知係唔係咁解題目,因為我係讀中文的) 3. In a test consisting of 20 multiple-choice questions. 5 marks will be given for a correct answer, 3 marks will be deducted for a wrong answer and no marks for unanswered questions. If Simon answered 16 questions in the test and got 56 marks, how many questions did Simon answer correctly? Let Simon answer x questions that is correct 5x-3(16-x)=56 5x-48+3x=56 8x=104 x=13 Simon has answered 13 questions correctly

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