Question Bank  100 Arithmetic Questions From Previous CAT Papers (Solved)

Solution: Let the maximum mark in each subject be 100. Hence, total marks (maximum) is 500, as there are 5 subjects.
Candidate obtained 60% of total marks, hence 60% of 500 = 300.
His individual marks were 6x, 7x, 8x, 9x and 10x.
So, total marks will be 6x + 7x + 8x + 9x + 10x = 40x
40x = 300.
x = 300/40 = 7.5
His marks are 6x, 7x, 8x, 9x and 10x.
So his marks were 45, 52.5 and all others are 50+ (as 7*7.5 itself is 50+)
So, 4 subjects he has 50+ marks out of 100, which means more than 50%.

Q21. (CAT 2001)
A can complete a piece of work in 4 days. B takes double the time taken by A, C takes double that of B, and D takes double that of C to complete the same task. They are paired in groups of two each. One pair takes twothirds the time needed by the second pair to complete the work. Which is the first pair?
a. A, B
b. A, C
c. B, C
d. A, D

Solution: In a day, A would do 1/4 th of work ; B would d 1/8th of work, C would do 1/16th of work, D would do 1/32th of work.
One pair would take > > 2/3 rd of time take by second pair.
Out of all combinations ; we get A+D together in a day can do 9/32 th of work.
B + C can do 3/16th of work.
3/16 = 2/3 * 9/32
B + C = 2/3 (A + D )
Hence the first pair is B,C and the second pair is A,D.Note: A, D or B, C should be the answer because for other combinations this ratio will be less than 1/2.now we can safely assume it to be A,D combination and start checking with it  saves time!

Q22 (CAT 1997)
A certain race is made up of three stretches: A, B and C, each 2 km long, and to be covered by a certain mode of transport. The following table gives these modes of transport for the stretches, and the minimum and maximum possible speeds (in km/hr) over these stretches. The speed over a particular stretch is assumed to be constant. The previous record for the race is 10 min.Mr Tortoise completes the race at an average speed of 20 km/hr. His average speed for the first two stretches is four times that for the last stretch. Find the speed over stretch C.
a. 15 km/hr
b. 12 km/hr
c. 10 km/hr
d. This is not possibleMr Hare completes the first stretch at the minimum speed and takes the same time for stretch B. He takes 50% more time than the previous record to complete the race. What is Mr Hare's speed for the stretch C?
a. 10.9 km/hr
b. 13.3 km/hr
c. 17.1 km/hr
d. None of theseAnshuman travels at minimum speed by car over A and completes stretch B at the fastest speed. At what speed should he cover stretch C in order to break the previous record?
a. Maximum speed for C
b. Minimum speed for C
c. This is not possible
d. None of these

Part 1 : Solution: Total distance = 2 + 2 + 2 = 6KM
Average speed for the whole journey = 20 KM/hr
Time taken = 6/20 = 0.3 hr > (1)
Speed for C = S
Then avg speed for A + B = 4S
Time taken for A + B = (2+2)/4S = 1/S
Time Taken for C = 2/S
Total Time = 1/S + 2/S = 0.3 ( from (1) )
=> S = 10 Km/hrPart 2 : Solution : Hare is taking 2/40 hours = 1/20 hours = 3 minutes each for first 2 sets.
Total time taken = 10 + 10/2 = 15 min.
Time taken for third set = 9 min.
2 km in 9 min for C  speed = 13.3kmphPart 3 : Solution : Previous record is 10 min.
Stretch A is covered at minimum speed  2 km at 40 kmph = 3 minutes
Stretch B is covered at fastest speed  2 km at 50 kmph = 2.4 minutes
Minimum time required to cover C = 2 km at 20 kmph = 6 minutes
So we cannot break the previous record!

Q23 (CAT 1997)
The Weirdo Holiday Resort follows a particular system of holidays for its employees. People are given holidays on the days where the first letter of the day of the week is the same as the first letter of their names. All employees work at the same rate.Raja starts working on February 25, 1996, and finishes the job on March 2, 1996. How much time would T and J take to finish the same job if both start on the same day as Raja?
a. 4 days
b. 5 days
c. Either (a) or (b)
d. Cannot be determinedStarting on February 25, 1996, if Raja had finished his job on April 2, 1996, when would T and S together likely to have completed the job, had they started on the same day as Raja?
a. March 15, 1996
b. March 14, 1996
c. March 22, 1996
d. Data insufficient

Part 1 : Solution: 1996 is a leap year.
Raja takes 7 days to complete the job (So our work package is 7 person days)
Now we'll apply Zeller's rule (Rule is explained as part of Q7) to determine that Feb 25th,1996 is a Sunday.
If T and J starts on Sunday, by Wednesday they can complete the work. (Sunday  2 Person days, Monday  2 Person days, Tuesday  1 Person day (T is on leave) and Wednesday  2 Person days)
So 4 days is sufficient.Part 2 : Solution: Raja doesn't have his name's first letter common to any of the day, so he won't rest.
He started his work on 25th Feb and finished on April 2 => He took 38 days to complete the job ( 1996 is a leap year) and he finished 1/38th of the work each day.Now S will take break on Saturday & Sunday and T will take a break on Tuesday & Thursday.
So every week each of them work for 5 days and together they work for 10 days.
so 10/38 of the work will be completed in one week. In three weeks they complete 30/38 of the work.Feb 25th, 1996 is a Sunday. (Refer Zeller's rule in Q7)
8 person days is required to finish the job.
Monday  Both work together  2 person days
Tuesday  Only S  1 person day
Wednesday  Both work together  2 person days
Thursday  Only S  1 person day
Friday  2 person days
So by Friday they will complete the work.
Total 21 + 6 = 27 days is required. March 22, 1996 would be the answer.

Q24. (CAT 2001)
If 09/12/2001 happens to be Sunday, then 09/12/1971 would have been a
a. Wednesday
b. Tuesday
c. Saturday
d. Thursday

Solution: Apply Zeller's rule directly and we'll get the answer as Thursday. Wait, if you don't know Zeller's rule then it is a very handy trick for Date related problems. Rule is explained below [credits  MathForum]
Zeller's Rule
Here's the formula:
f = k + [(13 * m1)/5] + D + [D/4] + [C/4]  2 * C.Eg: January 29, 2064 is a ?
 k is the day of the month. Let's use January 29, 2064 as an example. For this date, k = 29.
 m is the month number. Months have to be counted specially for Zeller's Rule: March is 1, April is 2, and so on to February, which is 12. (This makes the formula simpler, because on leap years February 29 is counted as the last day of the year.) Because of this rule, January and February are always counted as the 11th and 12th months of the previous year. In our example, m = 11.
 D is the last two digits of the year. Because in our example we are using January (see previous bullet) D = 63 even though we are using a date from 2064.
 C stands for century: it's the first two digits of the year. In our case, C = 20.
Now let's substitute our example numbers into the formula.
f = k + [(13 * m1)/5] + D + [D/4] + [C/4]  2 * C
= 29 + [(13 * 111)/5] + 63 + [63/4] + [20/4]  2 * 20
= 29 + [28.4] + 63 + [15.75] + [5]  40
= 29 + 28 + 63 + 15 + 5  40
= 100.Once we have found f, we divide it by 7 and take the remainder. Note that if the result for f is negative, care must be taken in calculating the proper remainder. Suppose f = 17. When we divide by 7, we have to follow the same rules as for the greatest integer function; namely we find the greatest multiple of 7 less than 17, so the remainder will be positive (or zero). 21 is the greatest multiple of 7 less than 17, so the remainder is 4 since 21 + 4 = 17. Alternatively, we can say that 7 goes into 17 twice, making 14 and leaving a remainder of 3, then add 7 since the remainder is negative, so 3 + 7 is again a remainder of 4.
A remainder of 0 corresponds to Sunday, 1 means Monday, etc. For our example, 100/7 = 14, remainder 2, so January 29, 2064 will be a Tuesday.

Q25. (CAT 2001)
At his usual rowing rate, Rahul can travel 12 miles downstream in a certain river in six hours less than it takes him to travel the same distance upstream. But if he could double his usual rowing rate for this 24 mile round trip, the downstream 12 miles would then take only one hour less than the upstream 12 miles. What is the speed of the current in miles per hour?
a. 7/3
b. 4/3
c. 5/3
d. 8/3

Solution: Let speed in stagnant water is x and speed of current=y.
12/(x  y)  12/(x + y) = 6..
1/(x  y)  1/(x + y) = 1/2
2y/(x^2y^2) = 1/2  (1)Similarly from second condition 2y/(4x^2  y^2) = 1/12  (2)
(1) / (2) = (4x^2  y^2)/(x^2y^2) = 6
2x^2 = 5y^2
Substituting this value in any of the condition we'll get y=8/3.
so option D

Q26. (CAT 2000)
A truck travelling at 70 kilometres per hour uses30% more diesel to travel a certain distance than it does when it travels at the speed of 50 kilometres per hour. If the truck can travel 19.5 kilometres on a litre of diesel at 50 kilometres per hour, how far can the truck travel on 10 litres of diesel at a speed of 70 kilometres per hour?
(1) 130
(2) 140
(3) 150
(4) 175

Solution: Diesel consumption increases by 30% for 70kmph speed. If diesel consumption is fixed (say 1 litre) then it'll go 19.5/1.3 = 15km when it's speed is 70kmph.
With 10 litres ,it will go 10 x 15 = 150 km.

Q27. (CAT 2000)
A, B, C are three numbers. Let
@ (A, B ) = average of A and B,
/ (A, B ) = product of A and B, and
X (A, B ) = the result of dividing A by B
Average of A, B and C is given by(1) @(/(@(/(B, A), 2), C), 3)
(2) X(@(/(@(B, A), 3), C), 2)
(3) /(@(X(@(B, A), 2), C), 3)
(4) /(X(@(/(@(B, A), 2), C), 3), 2)

Solution: Solve via options.
Simplify options further to see which one yield (A + B + C)/3
Only Option 4 does. (explained below)/(X(@ (/(@(B, A), 2), C), 3), 2) = /(X(@ (/(A+B)/2), 2), C), 3), 2)
= /(X(@ (A+B), C), 3), 2) = /(X((A+B, C)/2, 3), 2)
= /[(A+B+C)/6,2]
= (A + B + C)/3

Q28. (CAT 1999)
Forty per cent of the employees of a certain company are men, and 75% of the men earn more than Rs. 25,000 per year. If 45% of the company’s employees earn more than Rs. 25,000 per year, what fraction of the women employed by the company earn less than or equal to Rs. 25,000 per year?
a. 2/11
b. 1/4
c. 1/3
d. 3/4

Let say total number of employees = 100
So men employees = 40
Women employees = 100  40 = 60
75% of men earn more than 25,000 => 40 x 75/100 = 30 men.
45% of total employees earn more than 25,000 => 45 Employees
So 45  30 = 15 women earn more than 25000 which is 1/4th of the total women employee
=> 1  1/4 = 3/4th of the women employee earn less than 25000.Even though we wrote many steps for making the solution clear, this can be solved quickly in our mind with in 10 seconds.
Note: In most of the questions involving it would be easier to assume total as 100 and then solve.

Q29. (CAT 2000)
The table below shows the agewise distribution of the population of Reposia.Age Group Percentage Below 15 years 30 15  24 17.75 25  34 17 35  44 14.5 45  54 12.5 55  64 7.1 65 and above 1.15 The number of people aged below 35 years is 400 million. If the ratio of females to males in the ‘below 15 years’ age group is 0.96, then what is the number of females (in millions) in that age group?
a) 82.8
b) 90.8
c) 80.0
d) 90.0

If you look at the table, people aged below 35 years is 30 + 17.75 + 17 = 64.75% of the total population (which is given as 400 million)
So total population = 400 x 100 / 64.75 = 617.76 million
Female/Male (in below 15 years age group) = 0.96 : 1
Total population below 15 years age group = 617.76 x 30 / 100 = 185.33 million
Number of females = (0.96/1.96) x 185.33 million = 90.77 million (~ Option b)

Q30. (CAT 1999)
Navjivan Express from Ahmedabad to Chennai leaves Ahmedabad at 6.30 a.m. and travels at 50 kmph towards Baroda situated 100 km away. At 7.00 a.m. HowrahAhmedabad Express leaves Baroda towards Ahmedabad and travels at 40 kmph. At 7.30 a.m. Mr Shah, the traffic controller at Baroda realizes that both the trains are running on the same track. How much time does he have to avert a headon collision between the two trains?
a. 15 min
b. 20 min
c. 25 min
d. 30 min