Can someone help if I've done this right?

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victoria0212

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I tried to help my friend with a math question but I'm not sure if I've done it correctly.

The question follows: you deposit 15 000 kr (swedish currency) and the interest is 2.5%. You just leave your money, no new deposits or withdrawals. And the interest stays at 2.5% all the time. How long will it take to get 20 000 kr in your account?

This is how I did it: 20200526_201936.jpg
Is this even the correct way to think? I would highly appreciate help.
Btw, "svar" means "answer" and "år" means "years".
 
It seems you dropped a zero in [MATH]20000=15000\left(1+0.025\right)^n[/MATH]( in the 15,000)

[MATH]n=\frac{\ln \left(\frac{4}{3}\right)}{\ln \left(1.025\right)}[/MATH]Solving this gives me a different number than you got. (hint it's higher)
 
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amathproblemthatneedsolve said:
It seems you dropped a zero in [MATH]20000=15000\left(1+0.025\right)^n[/MATH]( in the 15,000)

[MATH]n=\frac{\ln \left(\frac{4}{3}\right)}{\ln \left(1.025\right)}[/MATH]Solving this gives me a different number than you got. (hint it's higher)
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Ah, yeah! Thanks for telling about the 0. I forgot one.
Can you please share what answer you got if I may ask?
 
I'll be more than happy too, can you just try to solve this:

[MATH]n=\frac{\ln \left(\frac{4}{3}\right)}{\ln \left(1.025\right)}[/MATH]
You're so close! I'll be interested to see what you get this time. (once I see what you've done I'll post the answer!) You weren't very far off it.
 
amathproblemthatneedsolve said:
I'll be more than happy too, can you just try to solve this:

[MATH]n=\frac{\ln \left(\frac{4}{3}\right)}{\ln \left(1.025\right)}[/MATH]
You're so close! I'll be interested to see what you get this time. (once I see what you've done I'll post the answer!) You weren't very far off it.
Click to expand...
Is it 11,65?
I think I got a different answer because I didn't use all the 3s
 
Why did you bother to reduce to 4/3 when you were going to approximate with 1.33. No, your answer was not incorrect because you did not use enough zeros? Why? Because there are NOT enough 3's to tack onto the end of 1.33 to get to 4/3. You might get close, but never get there. Just use 4/3 instead!
 
Jomo said:
Why did you bother to reduce to 4/3 when you were going to approximate with 1.33. No, your answer was not incorrect because you did not use enough zeros? Why? Because there are NOT enough 3's to tack onto the end of 1.33 to get to 4/3. You might get close, but never get there. Just use 4/3 instead!
Click to expand...
I saw explanations about it online from different math teachers etc. I simply tried to do what they did just to make myself understand it more etc. Haven't done this kind of math in a long time. But I understood it afterwards. Thanks for the input anyways ^^.
 
victoria0212 said:
I saw explanations about it online from different math teachers etc. I simply tried to do what they did just to make myself understand it more etc. Haven't done this kind of math in a long time. But I understood it afterwards. Thanks for the input anyways ^^.
Click to expand...
Funny how approximations can lead so far away from the answer using 11.54 gives you an end balance of $19,954.49.

;)
 
Regardless of what high school teachers may tell you, your answer and most intermediate work should not have decimals. Math is exact so why approximate the solution when you had the correct fraction.
 
Jomo said:
Regardless of what high school teachers may tell you, your answer and most intermediate work should not have decimals. Math is exact so why approximate the solution when you had the correct fraction.
Click to expand...
I will keep that in mind next time. We learn from mistakes I guess.
 
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