# Math Help - help with algebra formula

1. ## help with algebra formula

Hi,

I'm having difficulty with this formula.

12%=kei+((1-0.3)x(kei-4%)x(20/80))

I need to find the value of kei. The book I am working with tells me the answer is 10.8% but I can't work out how you get to that answer.

Any assisstance would be greatfully appreciated?

2. Originally Posted by mirimiri376
Hi, I'm having difficulty with this formula.

12%=kei+((1-0.3)x(kei-4%)x(20/80))

I need to find the value of kei. The book I am working with tells me the answer is 10.8% but I can't work out how you get to that answer.
Any assisstance would be greatfully appreciated?
Given: 12%=kei+((1-0.3)x(kei-4%)x(20/80))

Change % to decimal value
0.12 = kei + ( 0.70 x(kei-0.04)x(0.25))

some rearrangement
0.12 = kei + (kei-0.04)x(0.25x0.70)

reduction
0.12 = kei + (kei-0.04)x(0.175)

expand & simplify
0.12 = kei + 0.1750kei - 0.007
0.12 + 0.007 = 1.175kei
0.127/1.175 = kei

0.127/1.175 = 0.108085 = 10.8% = kei

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