IIT JEE , AIEEE Forum - Mathematics , Algebra

ashish_banga

AT WHAT TIME BETWEEN 2 O' CLOCK AND 3 O' CLOCK WOULD THE MINUTE HAND AND THE HOUR HAND BE THE REFLECTIONS OF EACH OTHER ABOUT THE VERTICAL AXIS IN A WALL CLOCK

mapqrs

2 . 44 o clock

srujana

let the required time as it is said that ( btw 2 n 3)

be 2 hrs x mins
in 1 hr hour hand moves through 30 deg

1 hr, minute hand moves through 6 deg
so

(2 + x/60). 30 = 360 - x.6

or x/2 = 360 - 6x

so x = 600 / 13

So ans is 2 hr 600/13 mins.

RyuAmakusa

srujana it's like your method but check it.

let the condition be met at 2 hrs.xminutes

in 60 min hr hand moves 30 degrees

in x min it moves x/2 defrees.

in 60 min min hand moves 360 degrees

in x min it moves 6x degrees.

now 60 + x/2 = 6x - 180

11x/2 = 240

x= 480/11 = 43.636....

it matches with

mapqrs ans

ayshwarya

hey frnd ryuamakusa can u explain d step

60 +x/2 =6x -180

im unable 2 understand it plzzzzzzzzzzz

RyuAmakusa

it would better with a diagram but i'l try to exp.

the req. time is after 2 o clock at 2 the hour hand is at 60 degree form 12

and x/2 is the angle moved in the x min.s

now angle moved by min. hand in x mins. is 6x. clearly 6x > 180 degrees from

12.now the 2 hands must be exactly opp. you join 12 and 6 and the hr. and

min. hand will will be a line segment now i have = ted the two vertically opp.

accute angles

ask me if not understood.

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