BENCHHMARK

Questions :

1. The ratio between the present ages of M and N is 4 : 5. If N is 4 years old than M, what will be the ratio of the ages of M and N after 4 years.

2. A certain sum of money is borrowed by arun at 10 % per annum for 15 years. If he pays an interest of rupees 300, then the total amount paid by arun.

3. In an examination, a pupil′s average marks were 63 per paper. If he had obtained 20 more marks for his Mathematics paper and 2 more marks for his Economics paper, his average per paper would have been 65. How many papers were there in the examination?

Answers :

1. Answer : 5 : 6

2. Answer : Rs. 200

3. Answer : 11

1. Explanation:

Let present age of M = 4x
Present age of N = 5x
N is 4 years old than M
5x = 4x + 4
5x – 4x = 4
x = 4
M′s age after 4 years = 4x + 4
= ( 4 * 4 ) + 4
= ( 16 + 4 )
= 20
N′s age after 4 years = 5x + 4
= ( 5 * 4 ) + 4
= ( 20 + 4 )
= 24
Ratio of their ages after 4 years = 20 : 24
= 5 : 6
∴ Ratio of their ages after 4 years is 5 : 6

2. Explanation:

Simple interest = ( Principal * years * Rate ) / 100
Simple interest = Rs. 300
Years = 15
Rate = 10 %
300 = P * ( 15 * 10 ) / 100
300 = P * ( 15 / 10 )
300 = P * ( 3 / 2 )
300 * 2 = 3 * P
( 600 / 3 ) = P
P = Rs. 200
∴ The total amount paid by arun is Rs. 200

3. Explanation:

Let the number of papers be x
His average mark = 63
His total mark = 63x
If he get 20 more marks in Mathematics and 2 more mark in Economics then the average will be 65
( 63x + 20 + 2 ) = 65x
22 = ( 65x – 63x )
22 = 2x
2x = 22
x = 11
∴ 11 papers were there in the examination.