Without any stoppage a person travels a certain distance at an average speed of 42km/hr and with stoppages he covers same distance at an average speed of 28 km/hr. How many minutes per hour does he stop?
Answer: D 42 km takes 60 minutes then 28 km will take = 60/42 * 28 = 40 minutes Average stoppage = 60-40 =20 minutes.
Q. No. 14:
A school has 4 sections of Chemistry in class X having 40,35,45 and 42 students. The mean marks obtained in chemistry test are 50,60,55 and 45 respectively for the 4 sections. Determine the overall average of marks per students.
Answer: B Required average = (40*50 + 35*60 + 45*55 + 42*45) / (40+35+45+42) => 52.25
Q. No. 15:
In an examination, a pupil's average marks were 63 per paper. If he had obtained 20 more marks for his Geography paper and 2 more marks for History paper, his average per paper would have been 65. How many papers were there in the examination?
Answer: C Let the number of papers be x. Then, (63x+22)/x = 65. On solving we get, x= 11.
Q. No. 16:
Ravi ate a number of toffees on each of the 5 week days of a certain week. On Tuesday, he ate 2 more than on Monday and 8 less than on Wednesday. On Friday, he ate 4 more than on Thursday and 6 less than on Wednesday. The average number of toffees he ate on the first three days and the last two days are in the ratio 4:3. Find the number of tofees he ate on Thursday?
Answer: B Let the number of toffees he ate on Monday =a The number of toffees he ate on subsequent days are from Tuesday to Friday are:- a+2, a+10, a, a+4 respectively. 3{(a+a+2+a+10)/3} = 4{(a+a+4)/2} => a=4.
Q. No. 17:
A cricket player played nine matches. The average number of runs he made per match was 16. His runs in the ith match were two less than that in the (i-1)th match. Find the average number of runs he made in the second and the eighth matches.
Answer: C Let the runs in the 1st match be a. The number of runs in the successive matches are :- a+4, a+6, a+8, a+10, a+12, a+14, a+16 The average of of 9 matches = (9a+72)/9 = a+8 =16.........(i) The average of second and the eighth match = (2a+16)/2 = a+8 Now from equation (i) it is equal to 16.
Q. No. 18:
In a group of 11 people, x is 32 years old and y is 4 years younger than x. If x and y are replaced by two other people, find the average age of the two people replacing x and y.
Answer: D Y's age is 32-4 = 28 Let the average age of 11 people be A. 11A = 32+28+k.....(i) Where k is the sum of remaining ages. 11(A-1) = a+b+k....(ii) where a and b are the ages of the two people replacing x and y. Substracting eq(ii) by eq(i).. 11 = 60 -(a+b) a+b = 49 (a+b)/2 = 49/2 = 24.5 years