Here's one more question I need help with.

Samir has some amount of rupees with him, the difference between $45.45$% and 36.36% of which is Rs. $789435689$. Find the amount.

a) $8683792579$

b) $8673792579$

c) $7573781479$

d) $88667292579$

e) None of these

Now, Samir is the name of Indian male, rupees is Indian currency and Rs. is symbol for Indian currency. You can try replacing those with $ and question will be the same. :)

Here's what I've done. I've subtracted $45.45$%-$36.36$%=$9.09$. I've multiplied $789435689*9.09/100$. Which should be answer, but it isn't and I don't know why. Am I doing something wrong?

The actual answer is a) $8683792579$.

Can anyone elaborate how its a) and if not, my method is correct or not?

Thanks in advance and really sorry for asking too many stupid questions. :(

  • $\begingroup$ Are these homework problems? If so, please say so in the question. $\endgroup$ – Aryabhata Aug 26 '10 at 17:10
  • $\begingroup$ Apparently they seem to be exam problems he missed, and he is now left wondering what went wrong. $\endgroup$ – J. M. is a poor mathematician Aug 26 '10 at 17:25
  • $\begingroup$ Actually I'm preparing for MBA and these problems are Quantitative Aptitude questions for my Central Admission Test, for which I'm going to appear in 2 months. Its similar exams like GMAT where you get math problems, tricky ones. I'm not from Math background and I've done my Engineering in Information Technology. There were some 15 questions in my task sheet (You can call it homework. Except the part, my teachers are not interested if I solve it or not, but I'm the one who really wanna solve), out of those I solved 12 and couldn't solve 3. I tried a lot, but couldn't. So I asked here. $\endgroup$ – Electrifyings Aug 26 '10 at 19:48
  • $\begingroup$ I'm not sure if double commenting is allowed or not, but last comment already exceeded the amount of characters, so I'm writing this one. Btw, is it okay if I ask such questions here? I mean I don't really wanna get banned for asking stupid questions. Kindly slap me whenever I'm asking idiotic questions. Thanks, I really appreciate your support guys. You've just made my day! (Night actually) :P $\endgroup$ – Electrifyings Aug 26 '10 at 19:50

789435689 is 9.09% or 9.09/100 of the whole amount—that is, $789435689=\frac{9.09}{100}x$ where $x$ is the whole amount—so you want to divide by 9.09/100 rather than multiplying by it.

It also may be worth noting that $0.\overline{36}=\frac{4}{11}$ and $0.\overline{45}=\frac{5}{11}$, so $0.\overline{09}=\frac{1}{11}$, so you are essentially multiplying by 11, which can be done by multiplying by 10 and adding the original number or by writing two copies of the number, shifted one place, and adding:

+ 789435689
  • $\begingroup$ Ohh, thanks for pointing that out and stating it in the form of equation. I feel idiot for hurrying things even though I knew it has something to do with the 1/11 value being 9.09. Sorry, I confused it with multiplication instead of actually doing division. Sorry for all the trouble you have to go through because of me. $\endgroup$ – Electrifyings Aug 26 '10 at 19:43

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