(Q3).A ladder has rungs 25 cm apart. The rungs decrease uniformly in length from 45 cm at the bottom to 25 cm at the top. If the top and the bottom rungs are 2
1
2
m apart, what is the length of the wood required for the rungs. [Hint: Number of rungs =
250
25
+ 1]

25 cm212m25 cm45 cm

Given: A ladder with rungs separated by a distance of 25 cm.

Total distance between the rungs = 2
1
2
m = cm
∴ Number of rungs =
250
25
+ 1 = + 1 =

Length of the bottom and top rungs = 45 cm and 25 cm

where a = 45; last term l = a11 = 25 and d = 2 cm

∴ Sn =
n
2
(a + l)
=
2
( + )
=
2
×

= ×

= cm

∴ Length of wood required for total rungs = cm.