2. Find the percentage change in each of the following questions.
(a) A quantity is decreased by 5% and then
increased by 80%
Solution: Let x be the original quantity.
(b)A quantity is decreased by 22% and then
increased by 25%
F.3 percentage
2014-10-05 5:55 pm
回答 (3)
2014-10-05 7:17 pm
✔ 最佳答案
2.(a)
Let x be the original quantity.
The final quantity
= x(1 - 5%)(1 + 80%)
= x(0.95)(1.8)
= 1.71x
The percentage change
= [(1.71x - x)/x] * 100%
= +17.1%
(increase 17.1%)
(b)
Let x be the original quantity.
The final quantity
= x(1 - 22%)(1 + 25%)
= x(0.78)(1.25)
= 0.975x
The percentage change
= [(0.975x - x)/x] * 100%
= -2.5%
(decrease 2.5%)
2014-10-05 8:42 pm
做percentage 要留意d.p.轉換呀！要小心d。
2014-10-05 6:01 pm
2) a)
DECREASED by 5%
x * (100%-5%) = x * 95% = x * 0.95
then INCREASED by 80%
x * 0.95 * (100% + 80%) = x * 0.95 * 180% = x * 0.95 * 1.80
= x * 1.71
2) b)
DECREASED by 22%
x * (100%-22%) = x * 78% = x * 0.78
then INCREASED by 25%
x * 0.78 * (100% + 25%) = x * 0.78 * 125% = x * 0.78 * 1.25
= x * 0.975
DECREASED by 5%
x * (100%-5%) = x * 95% = x * 0.95
then INCREASED by 80%
x * 0.95 * (100% + 80%) = x * 0.95 * 180% = x * 0.95 * 1.80
= x * 1.71
2) b)
DECREASED by 22%
x * (100%-22%) = x * 78% = x * 0.78
then INCREASED by 25%
x * 0.78 * (100% + 25%) = x * 0.78 * 125% = x * 0.78 * 1.25
= x * 0.975
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