maths 20 may 2
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Maths for competitiveMaths for competitiveexamexam
Dr. T.K. Jain.Dr. T.K. Jain.
AFTERSCHOOOLAFTERSCHOOOLM: 9414430763M: 9414430763
tkjainbkn@yahoo.co.intkjainbkn@yahoo.co.in
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By selling 45 oranges for Rs. 160 aman loses 20%, how many should hesell for Rs. 112 to gain 20% on the
whole? Selling price of 45 oranges = 160 (which is
80% of cost)
Cost of 45 oranges = 160*(100/80)=200,to earn 20%, he should have sold for 240.He has suffered a loss of Rs. 80, so firstrecover that loss. 112-80 = 32. he can sell
45 oranges in Rs. 240, so how many can hesell for Rs. 32 = 32/240(45) = 6 oranges.
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The average salary per head of allemployees of a company is Rs. 600. the
average salary of 120 officer is Rs. 4000.If the average salary per head of rest ofthe employees is Rs. 560, find the total
number of workers in the company?
Total salary of all the employees = 600x Salary of remaining persons = 560*(x-120) We already know about total salary of officers = 120*4000
= 480000 560(x-120) = 600x- 480000
560x-67200 =600x-480000 -40x = -480000 + 67200 X= 412800/40 = 10320, so other employees are 10200 Ans.
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In a lottery there are 10 prizes and 25blanks, what is the probability of
getting a prize?
10 / 35 Ans.
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There are two urns. First contains 9white, 7 red and 4 black balls. The
second contains 4 red, 5 white and 5
black balls. First we take a ball fromfirst urn and put it in the second urnand then we draw a ball from secondurn. What is the probabilty that we
draw a red ball from second urn?
Red from first box and second both: 7/20
*5/15 = 7/60 OR Other colour from first and red fromsecond: 13/20*4/15 = 13/75
Probability = 7/60+13/75 = .29 approx.
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A cone, a hemisphere and a cylinderstand on equal bases and have sameheight. What is the ratio of their
volume? Cone: pie* 1/3 *radius*radius*height
Hemisphere : 2/3 *pie*r^3
Cylinder: pie*r^2*h R is same in each case and height is
equal to radius. So the volumes are in
ratio of 1:2:3 ans.
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The ratio between the volume of asphere and volume of a circumscribing
right cylinder is? Formulae : sphere: 4/3 pie r^3 Cylinder: pie *r^2*h Let radius of sphere = 1
Volume: 4/3 pie Height of cylinder: 2 because it is double
of radius (2* radius of sphere) Volume of cylinder: 2 pie Ratio: 2:3 Ans.
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Cost of fencing a square garden is Rs.400 @ re. 1/- per meter. The area of
the garden is ? Perimeter is = 4*side
Perimeter is 400, one side = 400/4
One side of square is 100. So he area is 100*100 = 10000 sqmts.
i
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atio o t e areas o twosquares is 9:1, what is the
ratio of their perimeter? Their sides would be in ratio of 3:1
Their perimeter will also be in ratio
3:1 ans.
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e eng an rea o a rec angu arfield are 120 and 80 meters respectively.Inside the field, a park of 12 m. width ismade around the field, what is the area of
park? Area of field: 120*80 = 9600
Area of field after deducting park
(120-24)*(80-24) = 96*56 =5376 Area of park = 9600-5376=4224 Ans.
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Cost of carpeting a room 15 meter longwith a carpet 75 cm. wide at 30 paise
per meter is Rs. 36, what is breadth of
the room? Total length of carpet used : 36*(100/30)
= 120 meters
Total area of carpet = .75*120 = 90sq.meters
Formulae of area = length*breadth
Area of room is equal to area of carpet, so
breadth of room = 90/15 = 6 Ans.
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Cost of coloring four walls of a room is Rs.500. another room has length, breadth and
height just double of this room. What will be
cost of coloring in that room? Ans : 2000
Remember the formulae
2*(length+bredth)*height Now all are doubled
2*(2l+2b)*2h = so new cost will befour times.
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I buy Rs. 25 shares which gives 9%dividend but for me it is 10% return, at
what price did I buy the shares? Dividend = 9% of 25 = 2.25 This is 10 % return for me, that
means I have invested 22.5 for thisshare. Thus I purchased these shares at
22.5 (at a discount of 2.5 from facevalue).
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True discount on 1860 due after a certaiintime at 5% is 60, what is the time of the
instrument? Present value is 1800 (1860-60)
Interest rate is 5% and interest is 60
One years interest is 90, eight monthinterest is Rs. 60 so answer is 8 month.
Remember, true discount is equal tointerest on present value.
T i t i
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True iscount on a i oRs. 540 is Rs. 90, what is
bankers discount on that? Present value is 540-90 = 450, 90 on 450 is 20%,
Thus 20% interest rate has beenused. Bankers discount is interest on face
value. So 20% of 540 is 108 Ans = 108.
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Bankers gain on a sum due 2 yearshence at 5% is Rs. 8. what is the
present value? Remember, bankers gain is simple
interest on true discount.
So true discount = 8*(100/5) = 160/2(as period if 2 years) = 80
Present value = 80*(100/5) = 1600
Ans: 1600
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Bankers discont on some money is 36and true discount is 30, what is the
bill amount, bankers gain and rate? Bankers gain = 36-30 = 6
6 is 20% of 30 so rate is 20%.
Bill amount is 36*(100/20) = 180 Present value is 30*(100/20) = 150
A f R 100 d it d t
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A sum of Rs. 100 deposited atcompound interest doubles after 5
years, what will be the amount after
20 years? After 5 years twice, after 10 years,
4 times, after 15 years, 8 times and
after 20 years 16 times. Thus the amount will be 1600 ans.
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