✔ 最佳答案
1. Vicky is 5 years older than Teddy. Four years later, Teddy's age will be 3/4 of Vicky's. How old are they now?
Let the present age of Vicky be x, the present age of Teddy be y
x - y = 5...........................(1)
(x + 4)(3/4) = y + 4............(2)
From (1),
4x - 4y = 20.......................(3)
From (2),
( 3x + 12 )/4 = y + 4
3x + 12 = 4y + 16
3x - 4y = 4........................(4)
(3) - (4),
4x - 4y - 3x + 4y = 20 - 4
4x - 3x = 16
x = 16 //
Substitute x = 16 into (1)
16 - y = 5
y = 11 //
The present age of Vicky is 16, the present age of Teddy is 11
2. The denominator of a fraction is greater than the numerator by 7. If we add 5 to both of them, the fraction will be reduced to 1/2. Find the fraction.
Let the numerator be x, the denominator be y, the fraction be (x/y)
y - x = 7..............................(1)
(x+5) / ( y+5) = 1/2................(2)
From (2)
2( x+5 ) = y + 5
2x + 10 = y + 5
2x - y = -5
y - 2x = 5...............................(3)
(1) - (3),
y - x - y + 2x = 7 - 5
-x + 2x = 2
x = 2 //
Substitute x = 2 into (1)
y - 2 = 7
y = 9 //
The fraction is 2/9