問2題數學題~

1. Let xcm be the width of the rectangle and ycm be the length of the rectangle.
2x = y-------------(1)
2x + 2y =42 -----------(2)

By substituting (1) into (2),
2x + 2(2x) = 42
2x +4x =42
x=7

By substituing x=7 into (1)
y=14
Therefore the area of the rectangle is:
14 x 7
=98 cm square

2. Let a be the number of question Johnny has answered in section A and b be the number of questions he has answerd in section B respectively.

a + b =40----------(1)
2a + 3b =92-------(2)

From (1),
b=40-a--------(3)

By substituting (3) into (2),
2a + 3(40-a) = 92
2a +120 - 3a =92
-a = -28
a = 28
By substituting a =28 into (1),
a + b =40
b=40-28
b=12
Therefore Johnny has answered 28questions in section A and 12 questions in section B.

1, let x is the width.
(x+2x)2=42
3x=12
x=4
so the width is 4 cm and the length is 8 cm.
2, let the number of question he has answered correctly in section A and B are x and y respectively.
x+y = 40.....(1)
2x + 3y = 92....(2)
from (1), we have x=40-y ...(3)
sub (3) into (2), we have 2(40-y)+3y=92
80-2y+3y=92
80+y=92
y+12
sbu y=12 into (1), we have x+12=40
x=28