To find out the number of postcards the friend bought, we use the equation 1.25x + 1.25(x + 3) = 16.25, where x is the number of postcards the friend bought. Solving this equation, we found that the friend bought 10 postcards.
To determine how many postcards your friend bought, let's define a variable. Let x be the number of postcards your friend bought. Then you bought x + 3 postcards. Since each postcard costs $1.25, the total cost of your friend's postcards is $1.25x and yours is $1.25(x + 3). Together, you spent $16.25, so the equation we set up is:
1.25x + 1.25(x + 3) = 16.25.
To solve for x, first distribute the 1.25 across the parentheses: 1.25x + 3.75 = 16.25. Subtract 3.75 from both sides to get 1.25x = 12.50. Divide both sides by 1.25 to find x, which gives you x = 10. Your friend bought 10 postcards.
The equation you set up and solve is 1.25x + 1.25(x + 3) = 16.25, which simplifies to x = 10.