Question

S is the sum of 12, 8, 6, 4 and x. What is the value of x if x = 2/5S?
(Linear equations)

Answer 1

x = 20

Explanation:

Sum of 12, 8, 6, 4 and x is:

S = 12 + 8 + 6 + 4 + x = 30 + x

`(2)/(5)S = (2)/(5)\cdot 30 + (2)/(5)x\\\\=12 + (2)/(5)x\\\\\\\textrm{But left side is nothing but x}\\\\\textrm{So we get }x = 12 + (2)/(5)x\\\\\rm{Subtract $(2)/(5)x$ from both sides}\\\\x - (2)/(5)x = 12\\\\(3)/(5)x = 12\\\\x = (12 \cdot 5)/(3) \\\\x = 20\\\\`

Verify

12 + 8 + 6 + 4 + 20 = 50

(2/5) x 50 = 20