State Secondary Certificate – ( SSC BOARD )

Recommended Question & Answers for Class 7

1. Subtract the sum of x2 – 5xy + 2y2 and y2 – 2xy – 3×2 from the sum of 6×2 – 8xy – y2 and 2xy – 2y2 – x2.

The sum of x2 – 5xy + 2y2 and y2 – 2xy – 3×2 = (x2 – 5xy + 2y2) (y – 2xy – 3×2)
= (x2 – 3×2) + ( – 5xy – 2xy) + (2y2 + y2)
= – 2×2 – 7xy + 3y2 ………………….(1)

The sum of 6×2 – 8xy – y2 and
2xy – 2y2 – x2 = (6×2 – 8xy – y2) + (2xy – 2y2 – x2)
= (6×2 – x2) + ( – 8xy + 2xy) + (-y2 – 2y2)
= 5×2 – 6xy – 3y2 ………………. (2)

From (1) and (2)

(2) – (1) = (5×2 – 6xy – 3y2) – ( – 2×2 – 7xy + 3y2)
= 5×2 – 6xy – 3y2 + 2×2 + 7xy – 3y2
= (5×2 + 2×2) + ( – 6xy + 7xy) + ( – 3y2 – 3y2)
= 7×2 + xy – 6y2

2. The distance between two stations is 240 km. A train takes 4 hrs to cover this distance. Calculate the speed of the train ?

Distance between the two stations = 240 km
Time taken by the train to travel this distance = 4 hrs
Speed = Distance travelled
Time = 2404 = 60 km/hr

3. Unexpectedly some water sprinkled on a mirror while Madhu was shaving his face. Did he observe any difference in his image? If yes, explain why?

1. When water is sprinkled on a mirror the plane surface of the mirror is disturbed.

2. So, the clarity in the images goes away and due to reflection taking place in a scattered way, the image becomes dull arid unclear.