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Which value of x makes the following equation true? 7.8(x - 2) = -0.2x + 40.4

0 votes
Algebra help. Thanks in advance.
asked Mar 5, 2013 in PRE-ALGEBRA by payton Apprentice

2 Answers

+1 vote

7.8(x–2) = –0.2x+40.4

Multiply each side by 10

(7.8)(10) (x–2) =(10)(–0.2x+40.4)

78(x–2) =(10)(–0.2x+40.4)

Distribute terms using distributive property:  a( b – c) = ab+ac

78x– 156 = – 2x +404

Add 156 and 2x to each side.

80x = 560

Divide each side by 80

x  = 7 is true

answered Mar 5, 2013 by hussy Rookie
0 votes

7.8(x - 2) = -0.2x + 40.4
7.8x - 7.8 *2 = -0.2 x + 40.4
addition property of equality: if a = b then a + c = b + c
add 0.2x to each side
7.8x - 15.6 + 0.2x = -0.2x + 40.4 +0.2x
8x - 15.6 = 40.4
add 15.6 to each side
8x - 15.6 + 15.6 = 40.4 + 15.6
8x = 56
division property of equality: if a = b then a / c = b / c ( c not equal to zero)
divide each side by 8
x = 7.

answered Mar 6, 2013 by steve Scholar

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