There are 23 coins in a bank. All the coins are dimes and quarters. The total value of the coins is $3.80. How many dimes are there? How many quarters?

Question

australopithecus · Answer

You have two formulas
where dimes are y and quarters are x

we have the formula
0.25(x) + 0.10y = $3.80

and another formula
x+y = 23

australopithecus · Answer

substitute one equation into the other to solve for one of the variables then sub that variable back into one of the original formulas to solve

anonymous · Answer

Set up a system of equations.

$\ \huge x+y=23 $.
$\ \huge .25x + .10y = 3.8 $.

Now solve for x and y.

australopithecus · Answer

so
set

 x = 23 - y

0.25(23-y) + 0.10y = $3.80
now solve for y

once you have solved for y sub it back into one of the original equations to solve for x

australopithecus · Answer

doing this tells us where the graphs intersect and therefore the answer we are interested in