Ed bought eight 25cent stamps and fourteen 10cent stamps.
Substitution is replacing a variable with another variable for our ease of calculation.
According to the given question
Ed spent $3.40 for 22 stamps.
OR
340 cents for 22 stamps.
Let x be the no. of 25 cent stamp and y be the no. of 10 cent stamps.
∴ x + y = 22
Now, 25x + 10y = 340 ....(i)
substituting the value of y in terms of x in (i)
y = 22 - x.
25x + 10(22 - x) = 340
25x + 220 - 10x = 340
15x = 120
x = 8
So, no. of 25 cents stamp is 8 and the no. of 10 cent stamps is
(22 - 8) = 14.
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