Correct Answer - Option 1 : 20

**Given:**

Number of total girls = 8

Number of days = 16 days

Work = Stitching 20 bed sheets

Per day work = 4 hours

**Formula used: **

1.) MDH/W is constant.

2.) M_{1} × D_{1} × H_{1}/W_{1} = M_{2} × D_{2} × H_{2}/W_{2}

Where,

M → The number of men

H → The number of hours

D → The number of days

W → The amount of work

**Calculation:**

Here, M_{1} = 8, H_{1} = 4, D_{1} = 16 and W_{1} = 20

Let the number of hours taken by 4 girls be h.

So, M_{2} = 4, H_{2} = h, D_{2} = 8 and W_{2} = 25

⇒ 8 × 4 × 16/20 = 4 × 8 × h/25

⇒ h = 20

**∴ 4 girls need to work for 20 hours a day. **