Question

Rajiv obtained 70 and 75 marks in first two unit tests. Find the minimum marks he should get in the third test to have an average of at least 60 marks.

Answer 1

Let x₁, x₂, x₃ denote the marks in 1^st, 2^nd, and 3^rd unit tests respectively.

Then `("x"_1+"x"_2+"x"_3)/3≥60`

∴ `(70+75+"x"_3)/3≥60`

∴ 145 + x₃ ≥ 3(60)

Subtracting 145 from both sides, we get

x ≥  180 – 145
∴ x ≥ 35
Rajiv must obtain minimum 35 marks to maintain average of at least 60 marks.