✔ 最佳答案
1. Let x be the denominator, then numerator is x+3.
original number = (x+3)/x
add 10 is (x+3+10)/(x+10) = (x+13)/(x+10)
then added result is (3/4) of the original number (x+3)/x
(x+13)/(x+10) = (3/4)(x+3)/x
x² + 13x - 90 = 0
(x+18)(x-5) = 0
x = 5 or x= -18 (reject < 0)
Original fraction is 8/5
add 10 = 18/15 = 6/5
(3/4)(8/5) = 24/20 = 6/5
2. Let v be the speed
original time needed = 240/v (h) 時間 = 距離 / 速率
timed need after adding speed = 240/(v+15)
time difference = 80/60 (h)
= 240/v - 240/(v+15)
80/60 = (240)(1/v - 1/(v+15)
v² + 15v -2700 = 0
v = 45 or v = -60 ( reject < 0)
240/45 = 5.33 hour
240/(45+15) = 4 hour
5.33-4 = 1.33 hour
1.33X60=79.8 minutes
