The total weight of a box, 20 plates and 30 cups is 4.8 kg. The total weight of the box, 40 plates and 50 cups is 8.4 kg. What is the total weight of the box, 10 plates and 20 cups?
+128474 20P + 30C = 4.8
40P + 50C = 8.4
Multiply the first equation by -2 add to the first and we have
-40P - 60C = - 9.6
40P + 50C = 8.4
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-10C = -1.2 divide both sides by -10
C = 1.2 / 10 = .12
And using 20P + 30C = 8.4
20 P + 30 (.12) = 4.8
20 P + 3.6 = 4.8 subtract 3.6 from both sides
20P = 1.2 divide both sides by 20
P = 1.2 / 20 = .6 / 10 = .06
So
10P + 20C =
10 ( .06) + 20 (.12) =
.6 + 2.4 =
3 kg
