Yusuf bought a DVD player for $280, now it is $220. What is the percent decrease in the price?

About 21.4%

Step-by-step explanation:

280 - 220 = 60

60 of 280 = ?

Variable x = percentage

60/280 = x/100

Cross multiply

60 × 100 = 280 × x

6000 = 280x

Divide both sides by 280

6000 ÷ 280 = 280x ÷ 280

21.428 = x

About 21.4%

Check work:

60/280 = 21.4/100

Cross multiply

60 × 100 = 280 × 21.4

6000 = 5992

6000 is close to 5992

It does not equal exactly 6000 because I estimated the percentage to 21.4% instead of 21.428%

answer: 204

step-by-step explanation:

we are told that the revenue is

x⋅(4080−10x)=−10x^2+4080x

this is a quadratic function, so to maximize it we should find the x-value of its vertex. recall that the x-value of the vertex of the parabola ax^2+bx+c is given by the formula −b/2a.

so in this case, we have a=−10 and b=4080, so the x-value of the vertex is

−b/2a= −(4080)/2(−10)=204