Question

if the same number be added to the numbers 5,11,15and 31. the resulting number are in proportion . FInd the number

Answer 1

Let the number be x

5+x/11+x = 15+x/31+x

=>(5+x)(31+x) = (11+x)(15+x)

=>153+5x+31x+x^2=165+11x+15x+x^2

(x^2 is deducted from each side)

=>36x+153=26x+165

=>36x-26x=165-153

=>10x=12

=>x=1.2