A hand fan is made by sticking 10 equal size triangular strips of two different types of paper as shown in the figure.

Given that,

The sides of AOB

AO = 25 cm

OB = 25 cm

BA = 14 cm

Area of each strip = Area of triangle AOB

Now, for the area of triangle AOB

Perimeter = AO + OB + BA

2s = 25 cm +25 cm + 14 cm

s = 32 cm

By using Heron's Formula,

Area of the triangle $A O B=\sqrt{s \times(s-a) \times(s-b) \times(s-c)}$

$=\sqrt{32 \times(7) \times(4) \times(18)}$

$=168 \mathrm{~cm}^{2}$

Also, area of each type of paper needed to make a fan = 5 × Area of triangle AOB

Area of each type of paper needed to make a fan $=5 \times 168 \mathrm{~cm}^{2}$

Area of each type of paper needed to make a fan $=840 \mathrm{~cm}^{2}$