Clare buys some shares for $50x. Later, she sells the shares for $(600 + 5x). She makes a profit of x% (a) Show that x^2 + 90x − 1200 = 0

Profit is (New price-Original price)/Original price . As a fraction it is percentage Profit/100. Equate (New price-Original price)/Old Profit to the fraction of Profit in %/100. Cross multiply and come up with a quadratic eqation. 0 (600+5x-50x)/50x=x/100 to give 100(600-45x)=50(x^2) Divide through by 50 2(600-45x)=(x^2) Move all on one side to end up with x^2 + 90x − 1200 = 0