Question

30 trees are planted in a straight line at intervals of 5m. To water them, the gardener needs to bring water for each tree, separately from a well, which is 10m from the first tree in line with the trees. How far will he have to walk in order to water all the trees beginning with the first tree? Assume that he starts from the well.

• A. 4785 m
• B. 4795 m
• C. 4800 m
• D. None of these

Answer 1

The correct option is B 4795 m

To find the sum of the series:
(10 + 10) + (15 + 15) + (20 + 20) + . . . + (150 + 150) + 155
= 2 (10 + 15 + . . . + 150) + 155
$=2\left[\frac{29}{2}\right(2\times 10+(29-1)\times 5]+155$
= 29 (20 + 140) + 155
= 29 $\times$ 160 + 155
= 4640 + 155 = 4795