Exercise 8D
Question 1
Increase:
(a) Rs. 50 by 20%
Sol :
$=\frac{20}{100}\times 50$
=10
∴New increased amount=50+10=60
(b) Rs. 700 by 8%
Sol :
$=\frac{8}{100}\times 700$
=56
∴New increased amount=700+56=756
(c) 600 g by 18%
Sol :
$=\frac{18}{100}\times 600$
=108
∴New increased amount=600+108=708g
(d) 4L by 15%
Sol :
$=\frac{15}{100}\times 4$
=0.6
∴New increased weight=(4+0.6)L=4.6 L
(e) 8 km by 19%
Sol :
$=\frac{19}{100}\times 8$
=1.52
∴New increased distance=(8+1.52)=9.52 km
(f) 5 kg by 23%
Sol :
$=\frac{23}{100}\times 5$
=1.15
∴New increased weight=(5+1.15)=6.15 kg
Question 2
Decrease:
(a) Rs. 170 by 10%
Sol :
$=\frac{10}{100}\times 170$
=17
∴New decreased amount=(170+17)=153
(b) Rs. 2500 by 18%
Sol :
$=\frac{18}{100}\times 2500$
=450
∴New decreased amount=(2500-450)=2050
(c) 1 ha by 28%
Sol :
$=\frac{28}{100}\times 1$
=0.28
∴New decreased amount=(1-0.28)=0.72 ha
(d) 12 tonnes by $24\frac{2}{3}$% tonnes
Sol :
$=24\frac{2}{3}\% \text{ of } 12$
$=\frac{74}{300}\times 12$=2.96
∴New decreased weight=(12-2.96)=9.04
(e) 24 m by 22%
Sol :
$=\frac{22}{100}\times 24$
=5.28
∴New decreased unit=(24-5.28)=18.72 m
(f) 480 g by 20%
Sol :
$\frac{20}{100}\times 480$
=96
∴New decreased weight=480-96=384 g
Question 3
The entrance fee at a science museum is Rs. 50. Senior citizens recieve a 20% discount. How much fee does a senior citizen pay?
Sol :
Discount for senior citizen$=2\left(50\times \frac{20}{100}\right)$=10
∴Fees for senior citizen=50-10=40
Question 4
What is the final price of a Rs. 4500 leather jacket that is on sale for 40% off?
Sol :
Discount price$=\left(\frac{40}{100}\times 4500\right)$
=1800
∴Final price of leather jacket=4500-1800=2700
Question 5
Increase Rs. 2000 by 10% and then decrease the new amount by 10%.
Sol :
∴Price increases$=\left(\frac{10}{100}\times 2000\right)$=200
∴New increased amount=(2000+200)=2200
New price decreases$=\left(\frac{2110}{100}\times 2200\right)$=220
∴New decreased amount=2200-220=1980
Question 6
Decrease Rs. 500 by 15% and then increase the result by 15%.
Sol :
∴Price decreases$=\left(\frac{15}{100}\times 500\right)$=75
∴Decreased price=500-75=425
New increased price$=\left(\frac{15}{100}\times 425\right)$=63.75
∴New increased price=425+63.75=488.75
Question 7
Find the per cent increase for the following.
(a) original price = Rs. 800, new price = Rs. 872
Sol :
Increased price=872-800=72
∴Percentage of new price$=\left(\frac{72}{800}\times 100\right)$=9%
(b) old income = Rs. 1,20,000, new income = Rs. 1,50,000
Sol :
∴Increased income=150000-120000=30000
∴Percentage of new income$=\left(\frac{30000}{120000}\times 100\right)$=25%
Question 8
Find the percent decrease for the following.
(a) From 500 to 100
Sol :
500-100=400
∴Decreased percentage$=\left(\frac{400}{500}\times 100\right)$=80%
(b) Original price = Rs. 300, new price = Rs. 270
Sol :
Decreased price=300-270=30
∴Decreased percentage$=\left(\frac{30}{300}\times 100\right)$=10%
Question 9
A property which was valued at Rs. 40,000 five years ago is now valued at Rs. 60,000. What is the percentage increase in value?
Sol :
Decreased value=60000-40000=20000
∴Percentage of increased value$=\left(\frac{20000}{40000}\times 100\right)$=50%
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