A ladder has rungs 25cm apart. The rungs decrease uniformly in length from45cm at the bottom to 25cm at the top. If the top and bottom rungs are 2.5m apart, what is the length of wood required for the rungs?
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the distance between top and bottom rungs = 2.5 m = 250 cms
total number of rungs the ladder has = 25 cms
the total number of rungs ( n ) = 250/25 + 1 = 10 + 1= 11
[ 1 is added because when the distance between rungs is divided by total rungs one rung will be left behind so it is added]
Sn= n/2 ( a + an)
=11/2 (45+25)
+11/2 ( 70)
= 11 (35)
= 385
therfore, total length of wood required for these rungs is 385 cm2.
Hope it helps.
total number of rungs the ladder has = 25 cms
the total number of rungs ( n ) = 250/25 + 1 = 10 + 1= 11
[ 1 is added because when the distance between rungs is divided by total rungs one rung will be left behind so it is added]
Sn= n/2 ( a + an)
=11/2 (45+25)
+11/2 ( 70)
= 11 (35)
= 385
therfore, total length of wood required for these rungs is 385 cm2.
Hope it helps.
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