Question

Two customers went to a post office to buy postcards and large envelopes. Each postcard costs the same amount, and each large envelope costs the same amount. The first customer paid $12 for 14 postcards and 5 large envelopes. The second customer paid $24.80 for 10 postcards and 15 envelopes. What was the cost in dollars of each large envelope?
A-$1.42
B- $1.15
C- $0.35
D- $0.63

Answer 1

The cost in dollars of each large envelope is $1.42.

Two equations can be derived from this question:

14p + 5l = 12 equation 1

10p + 15l = 24.80 equation 2

Where:

p = postcards

l = large envelopes

To determine the cost of large envelopes, multiply equation 1 by 10 and equation 2 by 14.

140p + 50l = 120 equation 3

140p + 210 = 347.20 equation 4

Subtract equation 3 from 4

227.20 = 160l

Divide both sides of the equation by 160

l = 227.20 / 160

l  = $1.42

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