The length of the rectangle is 20 cm, and the width is 15 cm. By what percentage will its area decrease if the length is reduced by 6 cm?

S = a * b
1) S1 = 20 * 15 = 300 (cm ^ 2)
2) 20-6 = 14 (cm) – new length
3) S2 = 14 * 15 = 210 (cm ^ 2) – new area
4) 300 cm ^ 2- 100%
210 cm ^ 2 – x%
Let’s compose and solve the proportion:
300/210 = 100 / x
x = 210 * 100/300
x = 70%
5) Was -100%
Became – 70%
100% – 70% = 30%
Answer: Its area will decrease by 30% if the length is reduced by 6 cm.