Question

i) There are 180 students in a class. The number of girls is 75. Find

the ratio of girls to the number of boys.

ii) Are 20,25,12,15 in proportion?

iii) The first, second and fourth term in a proportion are 32,112,217

respectively. Find the third term.

iv)Find the value of 3a²-ab+4b if a=8 and b=2
vi) Khushi purchased a book worth 156.65 rupees from a bookseller

and gave him a 500 rupee note. How much balance did she get

back?​

Answer 1

Answer:

i) 5:7

Total students = 180

no. of girls = 75

if no. of girls is 75 and total students are 180 then no. of boys => 180-75 = 105

now

75:105 (divide by 15)

5:7

ii) As 20/25 = 4/5 and 12/15 = 4/5

Yes 20, 25, 12, 15 are in proportion.

iii) In the question given the first 2 numbers are 32 and 112 (represented as a and b in the above equation.) and the 4th number is 217 (represented as d).

To find the 3rd number, c, we can write it as:

c = (a × d) ÷ b

  = (32 × 217) ÷ 112

  = 62

iv) ---

v) 500 - 156.65 = 343.35