[tex]Let \: Sale \: in \: 2010 \: =100[/tex]

[tex]let \: sale \: in \: \: 2011 = \: 80[/tex]

[tex]Required \: Increase \: = \frac{100 - 20}{20} \times 100[/tex]

[tex] = \frac{80}{20} \times 100[/tex]

[tex] = \frac{8000}{20} [/tex]

[tex] = 400\%[/tex]

Step-by-step explanation:

LetSalein2010=100

let \: sale \: in \: \: 2011 = \: 80letsalein2011=80

Required \: Increase \: = \frac{100 - 20}{20} \times 100RequiredIncrease=

20

100−20

×100

= \frac{80}{20} \times 100=

20

80

×100

= \frac{8000}{20}=

20

8000

= 400\%=400%