A battery can operate 8 toys for 21 hours. For how long could the battery operate 15 bears?

Question

anonymous · Answer

I was hope you would answer

anonymous · Answer

I have been messing arounf with it and I do have an answer

anonymous · Answer

i done 8*21=15x where x is the hours

callisto · Answer

@Hollywood_chrissy I was doing in the same way as you :S

anonymous · Answer

:) but I dont stand what I done.

diyadiya · Answer

A battery can operate 8 toys for 21 hours

so for 1 toy =21/8 hours 
15 toys =21/8 * 15 ?

anonymous · Answer

Less toys more time so it's inversely proportional.

Using unitary method:

8 toys for 21 hours
1 toys for 21*8 hours
15 toys in  $ (21\times8)/15 = \frac{56}{5} = 11.2 $  hours

diyadiya · Answer

Isn't 1 toy 21/8 hrs?

anonymous · Answer

If we use batteries of 8 toys in just 1 toy then the battery will last long. So more time.

diyadiya · Answer

OOOOh okay!!

anonymous · Answer

NO worries diya, I got deceived too :P

callisto · Answer

Here comes the question...Is it  8 toys for 21 hours each (total time = 8x12 hours )or 21 hours for 8 toys ... That's what I'm thinking of.... :S (personally i think it is the first case)

callisto · Answer

This question is somehow like the previous one you asked..

anonymous · Answer

@Hollywood_chrissy: Do you know the right answer? :)

kropot72 · Answer

Hollywood_chrissy and FoolForMath both have the correct answer. Increasing the number of toys will drain the single battery faster.

anonymous · Answer

can I get an good answer????

callisto · Answer

Assume you've got the correct numerical answer. Here is the explanation.
The total operating hours for the battery = 8x21 = 168 hours, understand this part?

anonymous · Answer

yes

callisto · Answer

Now, you have the same battery, that means the total operating hours for the battery remains unchanged, that is 168 hours. understand this part?

anonymous · Answer

yes

callisto · Answer

Then, you have 15 bears now. You want to use the battery to operate these 15 toys (equally), understand this part?

anonymous · Answer

yes

callisto · Answer

So let x be the number of operating hours per bear.
number of bear * number of operating hours per bear = total number of working hours
15 x = 168
Understand this part?

anonymous · Answer

yes

callisto · Answer

solve x and you'll get the answer you want.
By the way, is the answer correct?

anonymous · Answer

yes 11.2 hours

callisto · Answer

Good :) Do you understand it now?

anonymous · Answer

I do

anonymous · Answer

thank you once more.

callisto · Answer

Glad to hear :) and you're welcome :)