shobha's mathematics test had 75 problems 10 arithmetic 30 algebra

Question

shobha's mathematics test had 75 problems 10 arithmetic 30 algebra 35 geometry problems. although she answered 70%of arithmetic, 40%of algebra, 60%of the geometry problems correctly, she did not pass the test because she got less than 60% of the problems right. how many more questions she would have needed to answer correctly to earn a 60% passing grade

 

10*70x/100+30*40x/100+35*60x/100=45

or

10*70x/100+30*40x/100+35*60x/100=60/100

 

in this question i know answer but i want to know that in creating equation what and where i did mistake please explain me

Answer 1

75 problems

70% of 10 arithmetic = (70/100)(10) = 7 right

40% of 30 algebra = (40/100)(30) = 12 right

60% of 35 geometry = (60/100)(35) = 21 right

                                               ----------------

                                                          40    [check your addition]

        40 right of  75       or 40/75 = 53.3%

 

To get 60%, she needs   (60/100)(75) = x right     or x=45 right

 

She needs 45 - 40 =  5 more questions right to get 60% to pass

Answer 2

Shobha has 40 out of 70 questions correct. This is less than 60%, actually 57.14%

 

n represents the number of additional correct answers to get 60% or more.

 

(40 + n) / 70 ≥ 0.60       multiply both sides by 70

40 + n ≥ 42                    subtract 40 from both sides

n ≥ 2

 

To pass the test Shobha must get at least to more correct answers.