Question

37. In an examination, a student's average marks were 63. If he had obtained 20 more marks for his Geography and 2 more marks for his history, his average would have been 65. How many subjects were there in the examination? b. 13 a. 12 C. 11 d. 14​

Answer 1

(total mark/number of subjects)×100=63

(total mark+20+2)/(number of subjects)×100=65

(total mark+22)/number of subjects=0.65

let n be the total number of subjects

((0.63 of 100n)+22)÷(100n)=0.65

because he obtained only 63 percent from sum of all marks.(marks counted from 100)

(0.63×100n+22)÷(100n)=0.65

0.63+(22÷100n)=0.65

0.22÷n=0.65-0.63

0.22÷n=0.02

n=0.22/0.02

n=11

there were 11 subjects