In 25 hours A can copy 75 pages
In 1 hour A can copy 75/25 = 3 pages
In 25 hours (A and B) can copy = 135/27 = 5 pages

Correct Option: A

In 25 hours A can copy 75 pages
In 1 hour A can copy 75/25 = 3 pages
In 25 hours (A and B) can copy = 135/27 = 5 pages
∴ In 1 hour B can copy (5 - 3) = 2 pages
∴ B can copy 42 pages in 21 hours.

Average speed = 2t₁ x t₂/( t₁ + t₂)

Correct Option: B

Average speed = 2t₁ x t₂/( t₁ + t₂)
= (2x64x80)/(64+80)km
= (2 x 64 x 80 ) / 144 km/hr.
=71.11km/hr.

A 's 1 day's work = 1/4
B ' s 1 days's work = 1/12
(A+B) ' s day ' s work = 1/4 + 1/12

Correct Option: B

A 's 1 day's work = 1/4
B ' s 1 days's work = 1/12
(A+B) ' s day ' s work = 1/4 + 1/12
= (3 + 1)/12 = 4/12 = 1/3
Days required by A and B together to do the work = 1 / (A + B ) ' s day ' s work = 3 days

M₁ = 240, D₁ = 48, M₂ = 160 and D₂ = ?
According to the formula,
M₁D₁ = M₂D₂

Correct Option: D

M₁ = 240, D₁ = 48, M₂ = 160 and D₂ = ?
According to the formula,
M₁D₁ = M₂D₂
⇒ 240 x 48 = 160 x D₂
∴ D₂= (240 x 48)/160 = 72

Given, M₁ = 5, M₂ = ?, T₁ = 7, T₂ = 3,
W₁ = 35 and W₂ = 65
According to the formula,
M₁T₁W₂ = M₂T₂W₁

Correct Option: D

Given, M₁ = 5, M₂ = ?, T₁ = 7, T₂ = 3,
W₁ = 35 and W₂ = 65
According to the formula,
M₁T₁W₂ = M₂T₂W₁
⇒ 5 x 7 x 65= M₂ x 3 x 35
⇒ M₂ = (5 x 7 x 65)/(35 x 3) = 65/3 boys