Question

A ladder has rungs 25 cm apart .the rungs decrease uniformly in length from 45 cm to 25 cm at the top .if the top and bottom rungs are 2.5 metre apart , what is the length of the wood required for the rungs

Answer 1

distance between the top and bottom of rungs= 2.5m
=250cm
distance between 2 continuous rungs=25
so total number of rungs=250/25 +1=11
so, 
n= 11
d=25
a=45
l=25

sn=n/2(a+l)
sn=11/2(45+25)
=11/2(70)   
=11*35
thus sn = 385cm
length of wood required to make the rungs= 385 cm
 
hope it helps!!!

Answer 2

Hope this helps you...
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distance between the top and bottom of rungs= 2.5m
=250cm
distance between 2 continuous rungs=25
so total number of rungs=250/25 +1=11
so,
n= 11
d=25
a=45
l=25

sn=n/2(a+l)
sn=11/2(45+25)
=11/2(70)
=11*35
thus sn = 385cm
length of wood required to make the rungs= 385 cm