urgent! f3 percentage

Keela

2009-08-01 6:47 am

1.When the price of gasoline is increased by 12.5%, Mr Chan decreases the consumption of gasoline by 4%. Fing the percentage change in his spending on gasoline.

2.If the radius of a circle is increased by 10%, find the percentage increase in its area.

3.If the height of a triangle is increased by 30% while its base is decreased by 25%, what is the percentage change in its area?

4.Alcohol and water are mixed in the ratio of 4:1 in volume. If 15% of alcohol is evaporated, and an additional 30% of the original amount of water is added,
a)what is the ratio of alcohol to water in the final mixture?
b)that is the percentage change in volume of the mixture?

pls ans. in detail and explain briefly

回答 (1)

用戶9112

2009-08-01 7:08 am

✔ 最佳答案

1.
Let original price be P per unit consumption, and original consumption be X.
Original spending = PX
New price = P * (1 + 12.5%) = 1.125P
New consumption = X * (1 – 4%) = 0.96X
New spending = 1.125P * 0.96X = 1.08PX
Percentage change = (1.08PX – PX)/PX * 100% = 8% increased
2.
Original radius = r
Original area = (pi)r2
New radius = r * (1 + 10%) = 1.1r
New area = (pi)(1.1r)2 = (pi)1.21r2
percentage increase in its area = [(pi)1.21r2 – (pi)r2]/(pi)r2 * 100% = 21%
3.
Original height and base are H & B
Original area = HB/2 = 0.5HB
New height = H * (1+30%) = 1.3H
New base = B * (1-25%) = 0.75B
New area = (1.3H)(0.75B)/2 = 0.4875HB
percentage change in its area = (0.4875HB – 0.5HB)/(0.5HB) * 100% = -2.5%
4.
Let volume of alcohol and water be 4V and V respectively
New volume of alcohol = 4V * (1-15%) = 3.4V
New volume of water = V * (1 + 30%) = 1.3V
a)ratio of alcohol to water = 3.4 : 1.3 or 34/13 : 1
b) New volume = 3.4V + 1.3V = 4.7V
percentage change in volume (4.7V – 5V)/5V * 100% = -6%

👍 0 👎 0