Average - Study Mode

[#366] In an exam, the average marks obtained by Jhon in English, Math, Hindi and Drawing were 50. His average mark in Maths, Science, Social Studies and Craft were 70. If the average mark in all seven subjects is 58, his score in Maths was -
Correct Answer

(D) 74

Explanation

Solution: E + M + H + D = 50 × 4 = 200 M + S.S + S + C = 70 × 4 = 280 $$overline {{ ext{M}} + (M + E + H + D + S.S + S + C) = 480} $$ M + (58 × 7) = 480 M = 480 - 406 M = 74 marks

[#367] 30 pens and 75 pencils altogether were purchased for Rs. 510. If the average price of a pencil was Rs. 2, what was the average price of a pen ?
Correct Answer

(D) Rs. 12

Explanation

Solution: According to the question, 30 pens + 75 pencils = Rs. 510 Average price of a pencil = Rs. 2 Price of 75 pencils = 2 × 75 = Rs. 150 ∴ Price of 30 pens = 510 - 150 = Rs. 360 ∴ Average price of pen = $$frac{360}{30}$$ = Rs. 12

[#368] The average age of 30 students of a class is 14 years 4 months. After admission of 5 new students in the class the average becomes 13 years 9 months. The youngest one of the five new students is 9 years 11 months old. The average age of the remaining 4 new students is :
Correct Answer

(A) 10 years 4 months

Explanation

Solution: According to the question, Total age of 30 students = 30 × (14 years 4 months) = 30 × $$14frac{1}{3}$$ = $$frac{30 × 43}{3}$$ = 430 years Total age of (30 + 5) students
= 35 (13 years 9 months) = 35 × $$13frac{3}{4}$$ = $$frac{1925}{4}$$ years Total age of 5 students = $$frac{1925}{4}$$ - 430 = $$frac{205}{4}$$ = 51 years 3 months ∴ One of the new five student is = 9 years 11 months old ⇒ Remaining 4 students age = $$frac{{{ ext{41 years 4 months}}}}{4}$$ = 10 years 4 months

[#369] The average age of husband, wife and their child 3 years ago was 27 years and that of wife and the child 5 years ago was 20 years. The present age of the husband is :
Correct Answer

(A) 40 years

Explanation

Solution: Total age of husband, wife and their child at present = 3 × 27 + 3 × 3 = 90 years Total age of wife and child at present = 20 × 2 + 2 × 5 = 50 years Husband's age = 90 - 50 = 40 years

[#370] The average of 10 items was found to be 80 but while calculating, one of the items was counted as 60 instead of 50. Then the correct average would have been :
Correct Answer

(C) 79

Explanation

Solution: Accounting to the question, Incorrect number = 60 Correct number = 50 Difference = 60 - 50 = 10 (more) Difference '10' effects all the 10 items = $$frac{10}{10}$$ = 1 Old average = 80 New average = 80 - 1 = 79