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Answer:
Number of 10 cents = 18
Number of 20 cents = 10
Step-by-step explanation:
Let number of 10 cents be = x
Let number 20 cents be = y
Total number of coins = x + y = 28 -------- ( 1 )
Total amount in the box = 0.10 x + 0.20y = 3.80 ---------- ( 2 )
<em><u>Solve the equations to find x and y</u></em>
( 1 ) => x + y = 28
x = 28 - y
Substitute x in ( 2 )
( 2 ) => 0.10(28 - y) + 0.20y = 3.80
2.80 - 0.10y + 0.20y = 3.80
0.10 y = 3.80 - 2.80
0.10 y = 1.00
y = 10
Substitute y in ( 1 ) => x + y = 28
x + 10 = 28
x = 28 - 10
x = 18
The solution to this system is (x, y) = (8, -22).
The y-values get closer together by 2 units for each 2-unit increase in x. The difference at x=2 is 6, so we expect the difference in y-values to be zero when we increase x by 6 (from 2 to 8).
You can extend each table after the same pattern.
In table 1, x-values increase by 2 and y-values decrease by 8.
In table 2, x-values increase by 2 and y-values decrease by 6.
The attachment shows the tables extended to x=10. We note that the y-values are the same (-22) for x=8 (as we predicted above). That means the solution is ...
... (x, y) = (8, -22)
