Question 6 - Figure it out - Page 42, 43, 44 - Chapter 2 Class 7 - Operations with Integers (Ganita Prakash II)

Transcript

Question 6 In a test, (+ 4) marks are given for every correct answer and (– 2) marks are given for every incorrect answer. (a) Anita answered all the questions in the test. She scored 40 marks even though 15 of her answers were correct. How many of her answers were incorrect? How many questions are in the test?Marks for correct answer = +4 Marks for incorrect answer = −2 Total marks = 40 Number of correct answers = 15 Marks for correct answers = 15 × 4 = 60 Also, Marks for incorrect answer = (−2) × No. of incorrect answers Now, Total marks = Marks for correct answer + Marks for incorrect answer 40 = 60 + (−2) × No. of incorrect answers 40 − 60 = (−2) × No. of incorrect answers –60 + 40 = (−2) × No. of incorrect answers –(60 – 40) = (−2) × No. of incorrect answers −20 = (−2) × No. of incorrect answers (−2) × No. of incorrect answers = –20 No. of incorrect answers = ( −20)/(−2) No. of incorrect answers = 10 ∴ Total 10 incorrect answers were there And, Total questions in test = Correct questions + Incorrect questions = 15 + 10 = 25 Question 6 In a test, (+ 4) marks are given for every correct answer and (– 2) marks are given for every incorrect answer. (b) Anil scored (– 10) marks even though he had 5 correct answers. How many of his answers were incorrect? Did he leave any questions unanswered?Total marks = –10 Number of correct answers = 5 Marks for correct answers = 5 × 4 = 20 Also, Marks for incorrect answer = (−2) × No. of incorrect answers Now, Total marks = Marks for correct answer + Marks for incorrect answer −10 = 20 + (−2) × No. of incorrect answers −10 − 20 = (−2) × No. of incorrect answers −(10 + 20) = (−2) × No. of incorrect answers – 30 = (−2) × No. of incorrect answers (−2) × No. of incorrect answers = –30 No. of incorrect answers = (−30)/(−2) No. of incorrect answers = 30/2 No. of incorrect answers = 15 ∴ His incorrect answers were 15 Now, Total questions answered = Correct answers + Incorrect answers = 15 + 5 = 20 Since there are 25 questions in the test Number of questions left unanswered = 25 – 20 = 5