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11. Rs. 20 is the true discount on Rs. 260 due after a certain time. What will be the true discount on the same sum due after half of the former time, the rate of interest being the same?

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Solution:
S.I. on Rs. (260 - 20) for a given time = Rs. 20
S.I. on Rs. 240 for half time = Rs. 10
T.D. on Rs. 250 = Rs. 10
∴ T.D. on Rs. 260
= Rs. 10250  × 260
= Rs. 10.40
12. The interest on Rs. 750 for 2 years is the same as the true discount on Rs. 960 due 2 years hence. If the rate of interest is the same in both cases, it is:

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Solution:
S.I. on Rs. 750 = T.D. on Rs. 960
This means P.W. of Rs. 960 due 2 years hence is Rs. 750
∴ T.D. = Rs. (960 - 750) = Rs. 210
Thus, S.I. on R.s 750 for 2 years is Rs. 210
Rate=(100×210750×2)%=14%
13. The simple interest and the true discount on a certain sum for a given time and at a given rate are Rs. 85 and Rs. 80 respectively. The sum is:

Discuss
Solution:
Sum=S.I.×T.D.S.I.T.D.=85×808580=Rs.1360
14. The present worth of Rs. 1404 due in two equal half-yearly installments at 8% per annum simple interest is:

Discuss
Solution:
Required sum
= P.W. of Rs. 702 due 6 months + P.W. of Rs. 702 due 1 year hence
=Rs.[100×702100+8×12+100×702100+(8×1)]=Rs.(675+650)=Rs.1325
15. If the true discount on s sum due 2 years hence at 14% per annum be Rs. 168, the sum due is:

Discuss
Solution:
P.W.=100×T.D.R×T=100×16814×2=600Sum=(P.W.+T.D.)=Rs.(600+168)=Rs.768
16. A tradesman marks his goods 10% above his cost price. If he allows his customers 10% discount on the marked price. How much profit or loss does he make, if any ?

Discuss
Solution:
Let cost price of goods = Rs 100
Market price of goods
=110% of 100 =110100×100 = Rs. 110
After discount selling price of goods
=90% of 110=90100×110=Rs. 99
Loss = 100 - 99 = Rs. 1
Loss % = 1100×100=1%

Alternate :
Loss% = x×y100%Loss% = 10×10100=1%
17. A discount of 212%  is given to the customer on the marked price of an article. A man bought the article for Rs 39. The marked price of the article is = ?

Discuss
Solution:
Discount = 2.5%
=2.5100=140Discount Market Price
Market Price = Rs. 40
Discount = Rs. 1
Cost Price = 40 - 1 = Rs. 39
39 → 39 Actual Cost Price
40 → Rs. 40
18. The marked price of a watch was Rs. 720. A man bought the same for Rs. 550.80, after getting two successive discounts, the first 10%. What was the second discount rate ?

Discuss
Solution:
Market price of a watch = Rs. 720
After 1st discount
 = 90% of 720  = 90100×720=Rs. 648
Cost price of watch = Rs. 550.80
Difference
= 648 - 550.80
= Rs. 97.20
2nd discount=97.20648×100=9720648=15%
19. A shopkeeper marks his goods 20% above cost price, but allows 30% discount for cash payment. His net loss is ?

Discuss
Solution:
Let the cost price of goods = Rs. 100
Market price of goods
 = 120% of 100  = 120100×100 = Rs. 120
After discount selling price of goods
= 70% of 120
= Rs. 84
Loss = 10084=Rs.16Loss % = 16100×100=16%

Alternate :
Formula = x±y± x×y100Loss% = 203020×30100=106=16% (Loss)
20. The equivalent single discount for two successive discounts of 15% and 10% is = ?

Discuss
Solution:
Equivalent to a single discount
=15+1015×10100=251.5=23.5%

Alternate :
Market price = Rs.100Cost price = 100×85100×90100 = Rs76.5Difference = 10076.5=23.5Difference%=23.5100×100=23.5%