Respuesta :

First set it up as an inequality using x and y as the amount of coins

10x + 20y = 690

Now get x by itself on one side by subtracting y

10x = 690 - 20y

Divide by 10 on both sides

X = 69 - 2y

Now plug this value for x into a separate equation just showing the amount of coins
(X+y=45)

69 - 2y + y = 45

Now solve for y

69 - y = 45

-y = -24

Y = 24

Now plug this y value into the same equation to solve for x

X + 24 = 45

X = 21

To check this work add both values into the original equation and solve

10(21) + 20(24) = 690

210 + 480 = 690

690 = 690

Answer:

$10 coins: 21

$20 coins: 24

Step-by-step explanation:

So we can create 2 equations where

x = number of $10 coins

y = number of $20 coins:

x + y = 45

10x + 20y = 690

we can move equation 1 around so that we can get a value of x

x = 45 - y

now we can substitute x into the second equation

10(45 - y) + 20y = 690

450 - 10y + 20y = 690

10y = 240

y = 24

Now plug in y back into the first equation

x = 45 - y

x = 45 - 24

x = 21

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