Correct calculation of interest rates

Source Station B - "two senior sister apprentice Recorder" :

1 Flower chant:

Buy a mobile phone, the price is 5999, when the flower chant stage 12, each has 537 total is 6449, "fee" 449.92 (ie interest, equivalent consumer loans), interest rates are calculated as follows:

利率 = 手续费 / 本金
分12期就是1年
年化利率 = 449.92 / 5999  约等于 7.5%
月利率 = 449.92 / 12 / 5999 约等于 0.625%

but, above algorithm is wrong!
Staging secret is its real interest rate is not low! You are in repayment of principal each month, you may in fact owe the principal is less and less, but staging it from beginning to end in the beginning as you owe in principal amount of computing! Charge you interest.
Then the correct calculated as follows:

The first stage of the principal = Amount / (1 + r) + the amount of the second stage of / (+ R & lt. 1) ² + ... + i-th stage of the amount / (R & lt +. 1) ⁱ + 12 of the installment amount / ( + R & lt. 1) ^{12 is}
therefore:
5999 = 537 / (R & lt +. 1) + 537 / (. 1 + R & lt) ² + ... +537 / (R & lt +. 1) ^{12 is}
to give the correct solution: r = 14.4% (chiral really do not count good count, here is the result of the video, you can use matlab, it is very good at solving equations)
micro-channel program has a small internal rate of return calculator:

You can see six points, interest rate is 16.4%

So staging of interest is very high!

Up to 15%

2 millet

Original 1699 mobile phone, 12 minutes

real annual interest rate is 13.83%

3 Jingdong IOUs

Jingdong have a concept of "rate", like credit cards say "interest-free installment" really does not mean that there is no interest, in fact, is 0.05% of the daily "daily interest" forgive, but each issue of fees, but according to income is not wrong
but not interest rates, he is the fee for a vest only, that is Jingdong not only charge you a fee each issue, we charge you the rate, then the Jingdong real annualized interest rate than spending more is not only chant less, and even with IOUs on credit without opening IOUs will not see the specific list of service fees, rates

4 Suning

Phone 5999, 12 minutes, 59.99 interests of each,

the real annual interest rate is 23.7%

So spend approximately equal to the cost of millet chant <Jingdong <Suning

Here you can look at the end of the ~ ~ ~

Now I should know, and recorded:
staging phenomenon knowledge representation, its rampant nature I think a lot of people have been brainwashed consumerism, 2018 HSBC data show that per capita debt 127,900 yuan after the 90-month debt was 18.5 input times
ants gold dress published in 2018, "China pension outlook survey," young people under the age of 35 years 56% of people do not start saving money, and start saving 44% of the people can only exist inside the average monthly 1389 yuan that the majority of young people simply save money, rent, eat (eat wild game, ah ~)
a month do not have to money, save it to the fund, or to stocks!
Why do we feel the pain, because a dollar more desire than ability to
brand the biggest cost is marketing costs, the production cost is not the product!
A person is energy is limited, it can not be used to thinking big energy spent on trivial things, time to grow less.