RBI Grade B Officers 2017 jun Paper

(2) Let speed of boat in stillwater = x kmph.
Speed of current = y kmph.
∴ Rate upstream
= (x – y) kmph
Rate downstream= (x + y) kmph.
According to the question,

36

x+y

+

14

x−y

=4...(i)

20

x−y

+

24

x+y

=5...(ii)
By equation (ii) × 3 – (i) × 2,

60

x−y

−

28

x−y

=15–8
⇒

32

x−y

=7
⇒x–y=

32

7

From equation (i),

36

x+y

+

14×7

32

=4
⇒

36

x

+y+

49

16

=4
⇒

36

x+y

=4−

49

16

=

64−49

16

=

15

16

⇒x+y=

36×16

15

=

192

5

∴x+y+x–y=

32

7

+

192

5

⇒2x=

160+1344

5

=

1504

35

⇒x=

1504

70

≈21.5kmph