averages Model Questions & Answers, Practice Test for ssc chsl tier 1
The average marks in Science subject of a class of 20 students is 68. If the marks of two students were misread as 48 and 65 of the actual marks 72 and 61 respectively, then what would be the correct average ?
Answer: (c)
Difference of marks
= 72 + 61 – 48 – 65 = 20
Correct average marks
= 68 + $20/20$ = 68 + 1 = 69
In a class, there are 32 boys and 28 girls. The average age of the boys in the class is 14 yr and the average age of the girls in the class is 13 yr. What is the average age of the whole class ? (Rounded off to two digits after decimal)
Answer: (a)
Average age of the whole class
= ${32 × 14 + 28 × 13}/{32 + 28}$
= ${448 + 364}/60 = 812/60$ = 13.53yr
Average of five consecutive odd numbers is 95. What is the fourth number in descending order?
Answer: (e)
${x + x + 2 + x + 4 + x + 6 + x + 8}/5$ = 95
5x + 20 = 95 × 5 = 475
$x = {475 - 20}/5$ = 91
99, 97, 95, 93, 91
4th Number = 93.
The average weight of 12 crewmen in a boat is increased by $1/3$ kg, when one of the crewmen whose weight is 55 kg is replaced by a new man. What is the weight of the new men?
Answer: (e)
Let the initial avg. be x.
(12 × x – 55 + y) = $12x + 1/3$
12x – 55 + y = $12x + 1/3$
$y = 1/3 + 55$ = 55.33
The sum of the ages of a father and his son is 45 years. Five years ago, the product of their ages is 34. Find the present age of father.
Answer: (e)
Let the ages of father and son be x and (45 – x) years respectively.
Then, (x – 5) (45 – x – 5) = 34
⇔ (x – 5) (40 – x) = 34
⇔ $x^2$ – 45x + 234 = 0
⇔ (x – 39) (x – 6) = 0
⇔ x = 39 or x = 6.
∴ Father's age = 39 years and son's age = 6 years
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