age problem with a shortcut

eddy2017

eddy2017

Elite Member
Joined
Oct 27, 2017
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The following is a shortcut in case you get a problem like this type and you are taking a timed test. (Timed tests are the order of the day!).I am bringing it to the forum to ask tutors if they think this may apply to different varieties of age problems. Don't know what the formula would be if instead of 'after.... ' we have '_____ago'


Ram is 3 times as old as Shyam. After 15 years Ram will be twice as old than Shyam. Find their current ages.
First condition: After 15 years= x, x=15
Second condition: Ram will be twice as old=m, m= 2
Third condition(the n condition)= 3 times as….as, n=3
who is the youngest = Shyam ( if you have Shyam's age you only will need to multiply by 3 to get Ram's
formula to find the age of the youngest person
[math]x(m-1)/n-m[/math]
Sustituye valores
15(2-1)/3-2
15(3)/1
=15 Shyam is 15 yrs old

Ram is 3 times as old as Shyam, so
3(15)= 45; Ram is 45 yrs

thanks,
eddy
 
Jomo said:
Until you say why this work it is all nonsense to you.
Click to expand...
I thought along the same thing after watching the second problem where he is not consistent with the first formula. he uses the variables of the first to name some other unknowns i n the second. Did not like it. But curiosity does kill the cat., doth it not. lol thank you
 
eddy2017 said:
15(2-1)/3-2
15(3)/1 ........................................here you go again .........where are the parentheses ..... and there are more problems...............
Click to expand...
 
Last edited by a moderator:
okay, I am back home.
I will take it from the original equation in the problem. if this equation has a problem, please, let me know before I move on to solve it. I think it is good like this:

[math]2\left(\frac{5}{3}-1\right)+2\left(\frac{7}{5-1}\right)\div \frac{5}{3}-\frac{7}{5}[/math]
 
this is the original equation. All the grouping symbols are okay according to what I know. There is no need of grouping symbols in the denominator, or is there?.
Is this correct or not?.
 
eddy2017 said:
this is the original equation. All the grouping symbols are okay according to what I know. There is no need of grouping symbols in the denominator, or is there?.
Is this correct or not?.
Click to expand...
As such, if you have COPIED it correctly - then it is correct.
 
yes, I followed the problem. Don' forget that my main doubt was when he write the 8. I did not know how he got it. that prompted my question. But I am going to continue the operation because I am still not clear about the multiplicative inverse, that is, how it was applied.
this is the equation before he converted the 4/15 to its multiplicative inverse.
[math]\left(2\cdot \frac{2}{3}+2\cdot \frac{2}{5}\right)\cdot \frac{4}{15}[/math]
 
eddy2017 said:
[math]x(m−1)/n−m \neq x(m−1)/(n−m)[/math]
Click to expand...
You even wrote the formula wrong.
[math]2\left(\frac{5}{3}-1\right)+2\left(\frac{7}{5-1}\right)\div \frac{5}{3}-\frac{7}{5}\neq[2\left(\frac{5}{3}-1\right)+2\left(\frac{7}{5-1}\right)]\div \underbrace{(\frac{5}{3}-\frac{7}{5})}_{\text{add parenthesis!}}[/math]
 
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In the next step he switches to the multiplicative inverse of 4/15 and then he multiplies what is in parentheses by 15/4.
My question is . Can this be done and be mathematically correct. Just invert the fraction and just that. please, confirm
 
eddy2017 said:
yes, I followed the problem. Don' forget that my main doubt was when he write the 8. I did not know how he got it. that prompted my question. But I am going to continue the operation because I am still not clear about the multiplicative inverse, that is, how it was applied.
this is the equation before he converted the 4/15 to its multiplicative inverse.
[math]\left(2\cdot \frac{2}{3}+2\cdot \frac{2}{5}\right)\cdot \frac{4}{15}[/math]
Click to expand...
How did you get 4/15 over there...

It seems you are doing subtraction before division. A no-no without parentheses.
 
eddy2017 said:
In the next step he switches to the multiplicative inverse of 4/15 and then he multiplies what is in parentheses by 15/4.
My question is . Can this be done and be mathematically correct. Just invert the fraction and just that. please, confirm
Click to expand...
no it is not wrong. have you watched the video?. please do. we are not on the same page. I am copying verbatim what the teacher did in the video.
 
have you watched that part in the video?. i understand everything because i have watched the video. have you?. please, answer me this question. we have been going back and forth about an equation that i have copied exactly from a video. i don't think you have watched the video
 
the equation before he substituted values is:
[math]m\left(x-1\right)+n\left(y-1\right)\div x-y[/math]
 
that is the equation the first one he set up and then he started substituting with the values he had given the variables and hence we have the equation that i wrote above. but i did not know where the 8 at the end came from. jomo explained later saying that he factorized the expression, but i was also in doubt about the way he used the multiplicative inverse. that is all
 
i know it is like that but i did not know how to write in that notation .that is why i used the division symbol. that was not my equation. i just copied it from the teacher. i may have not expressed it well because the la tex but i know it is like that. what are you all talking about. i asked only how the 8 came about. that was my only doubt. the only thing i did not understand when he performed the calculations. that is why i kept asking myself if he had done something wrong because i had even sent you the video for you to watch and then jomo said, oh no he factor the blessed thing, and then i got it!!!
 
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