1.if the number of a certain kind of germs increases by 40% every half an hour,by what percentage will the number of germs of that kind increase after 2 hours?
2.johnny has deposited a sum of money in a bank on simple interest at the beginning of year 2010.the interest rate is 3% p.a. for the first year and 4% p.a. thereafter. if he will earn an interest of $880 after 3 years,
a) find the sum of money deposited in the bank.
b)in which month and year will he obtain an amount of $10000
F.3 percentage
2011-03-14 12:03 am
回答 (1)
2011-03-14 1:14 am
✔ 最佳答案
1. (1+40%)^4=1.4^4
=3.8416 x100%
=384.16%
2.a) Let x be the sum of money deposited in the bank
x(3%)+x(4%)+x(4%)=880
0.03x+0.04x+0.04x=880
0.11x=880
x=8000
Johnny has deposited $8000 in the bank.
b) Let y be the years he will obtain the interests $ 100000.03(8000)+(0.04)(8000)y=10000
240+320y=10000
320y=9760
y=30.5
Johnny will obtain an interests of $10000 after 30.5 years (30 years and 6 months)
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