Question

1. A ladder 4 1/2 m long has rungs at a distance of 7.5 cm from each other. How many rungs does the ladder have?

2. A sofa set costs Rs.2,200 per seat. A man wants 5 1/2 seats. How much will it cost him?

Note: 4 1/2 and 5 1/2 are in mixed fraction.

Answer 1

Answer:

It is given that the rungs are 25 cm apart and the top and bottom rungs are 2

2

1

m apart.

∴ the total number of rungs.

25

2

2

1

×100

+1

=

25

250

+1=11

Now, as the lengths of the rungs decrease uniformly, they will be in an A.P.

The length of the wood required for the rungs equals the sum of all the terms of this A.P.

First term, a=45

Last term, l=25

n=11

S

n

=

2

n

(a+l)

S

10

=

2

11

(45+25)=

2

11

×70=385 cm