Help me solve these problems... Plz.....?

1)
Let the no of correct answers = x
and the no. of wrong answers = y
x + y = 30 (questions attempted)
3x - 2x = 40 (marks obtained)

Solving these two equations, we get x = 20 and y = 10

2)
Let the present ages be 3x and 5x
After 10 years, their ages will be (3x + 10) and (5x + 10)
The ratio is (3x + 10) / (5x + 100 = 5 / 7
Cross multiplying 21x + 70 = 25 x + 50 ==> 4x = 20 and x = 5
The present ages of A and B are , 3*5 = 15 yrs and 5*5 = 25 yrs

3) let the width of path be x meters
Then the inner dimensions of the rectangle are (166 - 2x) m and (68 - 2x)
Area of rectangular field (outer) = 166 * 68 = 11288 sq. m
Area of inner rectangle (without path) = (166 - 2x) * (68 - 2x) = 11288 -234 x + 4 x^2
Area of path = area of outer rectangle - area of inner rectangle
= 11288 -(11288 - 468 x - 4 x^2) = 720
==> 468 x - 4x^2 = 720 ==> x^2 - 117 x + 180 = 0
This is a quadratic equation. Solving by quadratic formula,

x = 1.56 m or x = 115.44 m
width of path cannot be 115.44 m, so the width of path = 1.56 m (approximately)

Then the area of path = (166*68) -

2) Let the ages be 3x : 5x

=> 10 years later --> 3x + 10 and 5x + 10

so, 3x + 10 = 5n and 5x + 10 = 7n

=> 5n - 3x = 7n - 5x

=> 2n = 2x

i.e. n = x

then, 3x + 10 = 5x or 5x + 10 = 7x

so, x = 5

=> ages now --> 15:25.......then, in 10 years --> 25:35

:)>

1.moan 20 answer were correct and 10 answere wrong .
as ,total answer given=30
correct answer given =20 and 3 marks for each answer =20 into 3=60
wrong answer given =10 and 2 marks for each answer =10 into 2 =20
so total marks =correct - wrong
= 60-20
=40 marks