There are two sets of traffic lights outside Eric's house. One day, he times how often they change. Set A turns green every 60 seconds. Set B turns green every 70 seconds. At midday precisely they both turn green together. At what time will they both turn green together again?

Pls I need help, I'm stuck

12:07pm

Step-by-step explanation:

first common multiple of 60 and 70 is 420

420 s = 7 mins

3. parallelogram

step-by-step explanation:

we turn each of our sides into direction vectors

ab=b-a=(3 - 7, 1 - 0) = (-4, 1)

bc=c-b=(1,6)

cd=d-c=(4,-1)

da=a-d=(-1,-6)

we see how the opposite sides have negated direction vectors; this is characteristic of a parallelogram.   we have congruent sides ab=cd and bc=da with unequal lengths because 1^2+6^2 is different from (-4)^2+1^2.   so it's not a square or a rhombus.  

we check the dot product of direction vectors of adjacent sides.   we have

ab dot bc = -4(1) + 1(6) = 2

that's not zero so the sides are not perpendicular.   we've ruled out rectangle.

the direction vectors indicate two pairs of congruent parallel sides, so we choose parallelogram over trapezoid.

60

step-by-step explanation: