loaning money for not exact months

[lino1000]

so there is a little math problem about people loaning money. my problem is i dont know how exactly to solve it when the time isnt in exact months (for example 42 days instead of 30 or 60) so here is my problem please help :

[FONT=&quot]Juan loaned Mary [/FONT]
[FONT=&quot][FONT=MathJax_Main]$[FONT=MathJax_Main]21[FONT=MathJax_Main],[/FONT][FONT=MathJax_Main]210[/FONT][/FONT][/FONT][/FONT][FONT=&quot] at an interest rate of [/FONT]
[FONT=&quot][FONT=MathJax_Main]5[FONT=MathJax_Main].[FONT=MathJax_Main]11[/FONT][FONT=MathJax_Main]%[/FONT][/FONT][/FONT][/FONT][FONT=&quot] for [/FONT]
[FONT=&quot][FONT=MathJax_Main]156[/FONT][/FONT][FONT=&quot] days. How much will Mary pay Juan at the end of [/FONT]
[FONT=&quot][FONT=MathJax_Main]156[/FONT][/FONT][FONT=&quot] days? Round your answer to the nearest cent. Note: [/FONT]
[FONT=&quot][FONT=MathJax_Main]360[/FONT][/FONT][FONT=&quot] days in a year and [/FONT]
[FONT=&quot][FONT=MathJax_Main]30[/FONT][/FONT][FONT=&quot] days in a month.[/FONT]

 

[Deleted member 4993]

so there is a little math problem about people loaning money. my problem is i dont know how exactly to solve it when the time isnt in exact months (for example 42 days instead of 30 or 60) so here is my problem please help :

Juan loaned Mary
[FONT=MathJax_Main]$[FONT=MathJax_Main]21[FONT=MathJax_Main],[FONT=MathJax_Main]210[/FONT][/FONT][/FONT][/FONT] at an interest rate of
[FONT=MathJax_Main]5[FONT=MathJax_Main].[FONT=MathJax_Main]11[FONT=MathJax_Main]%[/FONT][/FONT][/FONT][/FONT] for
[FONT=MathJax_Main]156[/FONT] days. How much will Mary pay Juan at the end of
[FONT=MathJax_Main]156[/FONT] days? Round your answer to the nearest cent. Note:
[FONT=MathJax_Main]360[/FONT] days in a year and
[FONT=MathJax_Main]30[/FONT] days in a month.

Interest rate to use =5.11% per year = 5.11/360 % per day = 0.014194% per day

 

[Harry_the_cat]

Interest rate to use =5.11% per year = 5.11/360 % per day = 0.014194% per day

Shouldn't that be 5.11/365 ??

Just saw the [FONT=MathJax_Main]360[/FONT] days in a year statement. Ummm.... NO!

Why do that? We all use calculators these days.

Reminds me of the "good ol' days" when textbooks were filled with circles where the radius was a multiple of 7, to make multiplying by pi = 22/7 easier!!

 

[stapel]

Just saw the [FONT=MathJax_Main]360[/FONT] days in a year statement. Ummm.... NO!

Not in "real life", no. But, in "business" math (and in business, in "real life"), often a 360-day year is used. In the context of simple-interest computations, this is called "ordinary" simple interest. A 360-day year is often called the "Banker's rule", for obvious reasons.

Why do that?

Because some aspects of the business world still use this, so business students (and the rest of us, too, arguably) need to be familiar with the difference between "exact" and "ordinary" interest.