model 2 net increase or decrease in % Practice Questions Answers Test with Solutions & More Shortcuts

Question : 11

The tax imposed on an article is decreased by 10% and its consumption increases by 10%. Find the percentage change in revenue from it.

a) 2% decrease

b) 11% increase

c) 1% decrease

d) 10% increase

Answer: (c)

Using Rule 3,

If an amount is increased by a% and then it is reduced by a% again, then the percentage change will be a decrease of $a^2/100$%

Special approach:

Required change = $(10)^2/100%$ decrease

= 1% decrease

Question : 12 [SSC MTS 2011]

When the price of cloth was reduced by 25%, the quantity of cloth sold increased by 20%. What was the effect on gross receipt of the shop?

a) 5% decrease

b) 10% decrease

c) 10% increase

d) 5% increase

Answer: (b)

Using Rule 5,

Required per cent effect = $(20 - 25 - {20 × 25}/100)%$

=(–5 – 5)% = – 10%

Negative sign shows decrease

Question : 13 [SSC FCI 2012]

A number is first increased by 10% and then it is further increased by 20%. The original number is increased altogether by

a) 15%

b) 36%

c) 32%

d) 30%

Answer: (c)

Using Rule 7,

Required percentage increase

= $(10 + 20 + {10 × 20}/100)%$= 32%

Question : 14 [SSC CGL Tier-II 2014]

If each side of a cube is increased by 10% the volume of the cube will increase by

a) 10%

b) 25%

c) 33.1%

d) 30%

Answer: (c)

Single equivalent increase for 10% and 10%

= $(10 + 10 + {10 × 10}/100)$% = 21%

Again, single equivalent increase for 21% and 10%

= $(21 + 10 + {21 × 10}/100)%$

= 31 + 2.1 = 33.1%

Using Rule 14,

"If every side of cube is increased by a%, then increase % in volume"

= $(3a + {3a^2}/100 + a^3/(100)^2)$%

Increase % in volume

= $(3 × 10 + {3 × 10^2}/100 + 10^3/(100)2)%$

=$(30 + 3 + 1/10)$ = 33.1%

Note : Volume of cube = $(Edge)^3$

Hence, formula $(x + y + {xy}/100)%$ should be used twice.

Question : 15 [SSC CGL Tier-1 2011]

When the price of an article was reduced by 20% its sale increased by 80%. What was the net effect on the sale?

a) 44% decrease

b) 75% increase

c) 66% increase

d) 44% increase

Answer: (d)

Using Rule 5,

Required effect = $(80 - 20 - {80 × 20}/100)%$

=(60 – 16)% = 44%

Positive sign shows increase.

IMPORTANT quantitative aptitude EXERCISES

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