Question

A ladder has rungs 25 cm apart.
(see Fig. 5.7). 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 25 m apart, what is
the length of the wood required for the
rungs?
250
Hint : Number of rungs = +1]
25​

Answer 1

Answer:

(The actual question has the top and bottom rungs 2.5m apart)

No of gaps = 2.5m/25cm =  10

So number of rungs is 10+1 =11

We know that  sum of n terms of AP is S=n/2(a+l) where l=last term=25cm and a=first term=45cm

and n=11

Thus Total length of wood required is S=11/2(25+45)=11/2(70) = 11 *35 =385cm