John has a total of 13 coins in his pocket. Of the 13 coins, they are all either quarters or dimes. The total value of the coins is $2.50. How many quarters does John have in his pocket?

Question

parthkohli · Answer

If john has x dimes, then he has 13 - x quarters(because x + 13 - x = 13)

parthkohli · Answer

Let's make an equation here.

$ \color{Black}{\Rightarrow x(10) + (13 - x)(25) = 250 }$

I expressed the $2.50 figure as cents.

anonymous · Answer

So, how would I figure that?

anonymous · Answer

The first step in solving this problem is to build two equations.
 0.25Q+0.10D=2.50 and Q+D=13 
where Q=total number of quarters and D=total number of Dimes. 
Next we try to subtract one equation from the other to eliminate one variable. 
So we multiply 0.25Q+0.10D=2.50 by 4 to get 1Q+0.4D=10. Then we subtract Q+0.4D=10 from Q+D=13. 
This results in 0.6D=3. We divide both sides by 0.6 and end up with d=5. 
Therefore we have 5 dimes, which equals 50 cents. 
Therefore we have $2 in quarters or 8 quarters. 
8 quarters is the answer.

anonymous · Answer

good enough

anonymous · Answer

did you really understand it ??? can you solve other such questions ???

anonymous · Answer

Sort of

anonymous · Answer

ok if i give you a similar question can you solve it ???

anonymous · Answer

Maybe

anonymous · Answer

I can try

anonymous · Answer

ok so here is a question:

anonymous · Answer

In a culture plate the number of bacteria initially was 2 times the number of virus in a second plate and there total sum is 50000. after an hour the their to total number becomes 100000 and in culture plate one bacteria become 4 times but the virus remains the same. calculate the original no of bacteria and virus ?

anonymous · Answer

@Kittyrae15  can you solve it

anonymous · Answer

ok let me make you the eq
no of virus = x
no of bacteria = y
x+2y=50000
after an hour
total = 100000
4(2y)+x=100000
x+8y=100000
now by substitution or elimination methods 
solve it.