Q1. Mr. A a dishonest dealer who professes to sell his goods at cost price, but he uses a weight of 900 gram instead for 1 kg. Find his gain%.
Calculation:
Error = 1000 gram – 900 gram
= 100 gram
Gain% = [100/(1000 – 100)] × 100
= [100/900] × 100
ANS =
Q2. If the difference between the compound interest and simple interest for 3 years at 10% per annum is Rs. 620. Find the principal amount ?
For 3 years,
C.I – S.I = P × (R/100)2 × [3 + (R/100)]
⇒ P × (10/100)2 × [3 + (10/100)] = Rs. 620
⇒ P × (1/10)2 × [3 + (1/10)] = 620
⇒ P × (1/100) × (31/10) = 620
⇒ P = 20,000
ANS = 20,000
Q3. In a town, population was 2,00,000 in 2015, it increased by 5% in 2016, by 6% in 2017, by 4% in 2018 and by 3% in 2019. Find the (approx.) population of the town in 2020 ?
Formula used:
P = PO [(1 + r1 / 100)] × [(1 + r2 / 100)] × [(1 + r3 / 100)] × [(1 + r4 / 100)]
Calculation:
P = 2,00,000 × [(1 + 5 / 100)] × [(1 + 6 / 100)] × [(1 + 4 / 100)] × [(1 + 3 / 100)]
= 2,00,000 × (105 / 100) × (106 / 100) × (104 / 100) × (103 / 100)
ANS = 2,38,449.12
Q4. A train without stoppage can travel at 60 km/h and with stoppage covers the same distance at 48 km/h. Find out the stoppage time of the train per hour.
Formula used:
Stoppage time = Difference of speed/Speed without stoppage
Calculation:
Stoppage time = (60 - 48)/60 hour
⇒ 1/5 hour
⇒ (1/5 × 60) minutes
⇒ 12 minutes
∴ The train stops for 12 minutes per hour.
SIMPLIFICATIONS TRICK
1. Multiplication with 5 : do 10/2
ex. 122 x 5 = 122 x 10/2
2. PERCENTAGE : DOUBLE AND HALF CONCEPT
EX. 15% OF 240 = 30% OF 120
3. (34 X 36) = (35-1) X (35+1) = a2 - b2 = (a + b)(a - b)
