AI Mentor

Check Your IQ

Free Expert Demo

Try Test

Courses

Dropper NEET Course Dropper JEE Course Class - 12 NEET Course Class - 12 JEE Course Class - 11 NEET Course Class - 11 JEE Course Class - 10 Foundation NEET Course Class - 10 Foundation JEE Course Class - 10 CBSE Course Class - 9 Foundation NEET Course Class - 9 Foundation JEE Course Class -9 CBSE Course Class - 8 CBSE Course Class - 7 CBSE Course Class - 6 CBSE Course

Offline Centres

Q.

The front compound wall of a house is decorated by wooden spheres of diameter 21 cm, placed on small supports. Eight such spheres are used for this purpose, and are to be painted silver. Each support is a cylinder of a radius 1.5 cm and height 7 cm and is to be painted black. The cost of paint if silver paint costs 25 paise per cmThe front compound wall of a house is decorated by wooden spheres of diameter 21 cm, placed on small supports. Eight such spheres are used for this purpose, and are to be painted silver. Each support is a cylinder of a radius 1.5 cm and height 7 cm and is to be painted black. The cost of paint if silver paint costs 25 paise per cmand black paint cost 5 paise per cmand black paint cost 5 paise per cmis

see full answer

Your Exam Success, Personally Taken Care Of

1:1 expert mentors customize learning to your strength and weaknesses – so you score higher in school , IIT JEE and NEET entrance exams.

An Intiative by Sri Chaitanya

a

Rs. 2784.25

b

Rs. 2785.25

c

Rs. 2787.25

d

Rs. 2789.25

answer is A.

(Unlock A.I Detailed Solution for FREE)

Best Courses for You

JEE

JEE

NEET

NEET

Foundation JEE

Foundation JEE

Foundation NEET

Foundation NEET

CBSE

CBSE

Detailed Solution

It is given, the compound wall of the house has 8 wooden spheres of 21cm diameter. And the support is a cylinder of a radius = 1.5 cm and height =7 cm.
To paint silver and black we need to find the surface area of the sphere and cylinder.
We know that, radius is half of the diameter.
Radius of sphere =

\frac{21}{2} cm

.
Surface area of a sphere

= 4 π r 2

. Surface area of 8 spheres,

= 8 × 4 × 227 × 2122 = 11088 c m 2

Surface area of top of cylinder is given by

π r 2

.
Surface area of the top of 8 cylinders,

= 8 × 227 × 1.5 2 = 56.57 c m 2

Surface area of spheres excluding base area is,
=

11088 − 56.75

=

11031.25

c m 2

The cost of paint of 1cm

silver paint =25 paise.
100 paise=1Rs.
25 paise=Rs.

25100

.
The cost of paint of

11031.25

c m 2

silver paint =

11031.25

×

25100

.
Surface area of a cylinder

= 2 π r h

.
Surface area of 8 cylinders,

= 8 × 2 × 227 × 1.5 × 7 = 528 c m 2

The cost of paint of 1cm

black paint =5 paise.
100 paise=1Rs.
5 paise=Rs.

5100

.
The cost of paint of

528 c m 2

black paint =528

×

5100

.
Total cost of the painting,

= 11031.25 × 25100 + 528 × 5100 = 11031.25 × 14 + 26.4 = R s .2784.25

.
Hence, the correct option is 1.

Watch 3-min video & get full concept clarity

courses

No courses found

Related Blogs

Get ₹ 1 crore* worth scholarship for JEE / NEET / Foundation

Result Producing online coaching for JEE/NEET of south India

Largest All India Test Series for JEE/NEET

Best Online Course for IIT JEE

Best Online Course for NEET

Best Online Course for CBSE

Ready to Test Your Skills?

Check your Performance Today with our Free Mock Test used by Toppers!

Take Free Test

Get Expert Academic Guidance – Connect with a Counselor Today!

Related Blogs

Get ₹ 1 crore* worth scholarship for JEE / NEET / Foundation

Result Producing online coaching for JEE/NEET of south India

Largest All India Test Series for JEE/NEET

Best Online Course for IIT JEE

Best Online Course for NEET

Best Online Course for CBSE

best study material, now at your finger tips!

live classes
progress tracking
24x7 mentored guidance
study plan analysis

download the app

gplay

mentor

Download the App

gplay

personalised 1:1 online tutoring