Question

5. Katie makes and sells scarves. Her monthly profit is given by P(s) = -s2 + 25s - 100, where "s" is the selling price. For what range of prices can Katie sell the scarves, in order to make a profit? (For what values of "s" will -s2 + 25s - 100 be greater than 0?)

Answer 1

Answer: s > 5

Explanation:

-s² + 25s - 100 > 0

Coefficient of s² is -1, multiply the equation through by -1.

-1 × (-s² + 25s - 100)

s² — 25s + 100

ax² + bx + c

Then you get the factors x and y that gives x + y = b and xy = c

b = -25 and c = 100, x = -20 and y = -5

-20 × -5 = 100 and -20 + -5 = -25

Then

s² — 20s — 5s + 100 > 0

Factorising,

s (s — 20) — 5(s — 20) > 0

(s — 5)(s — 20) > 0

(s — 5) > 0 and (s — 20) > 0

s>5 and s>20

s > 5

Hope this Helps?