Brain Grain · braingrain.in
Maths — Practice Paper · Set 1
Part I — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
1.One diagonal of a rhombus is twice as long as the other diagonal. If the rhombus has area $128\text{ cm}^2$[2]
2.Which term of the sequence $t_n = 5n - 3$[2]
3.An arc of a circle subtends an angle of 70° at the centre. What is the measure of the angle subtended by the arc at a point on the circle?[2]
4.Use the Baudhāyana–Pythagoras theorem to show why Theorem 6 must be true.[2]
5.Find the sum: (i) $\dfrac{2}{5}+\dfrac{3}{10}$[2]
6.Find the values of the following polynomials at the indicated values of the variables. (i) $5x^2 - 3x + 7$[2]
7.Look at the sequence of numbers on one column of the Ishango bone: 11, 13, 17, 19. What do these numbers have in common? List the next three numbers that fit this pattern.[2]
8.There are two fruit baskets A and B. Basket A has one apple and two oranges. Basket B has one banana and one mango. You randomly pick one fruit from each basket. (i) Draw a tree diagram showing all possible pairs of fruits. (ii) List the sample space. (iii) What is the probability of picking one apple and one banana?[2]
9.If the diameter of a car tyre is 56 cm, then: (i) How far does the car need to travel for the tyre to complete one revolution? (ii) How many revolutions does the tyre make if the car travels 10 km?[2]
10.Factor the following algebraic expressions: (i) $4y^2 + 1 + \dfrac{1}{16y^2}$[2]
11.The number $0.\overline{9}$[2]
12.We know that Natural Numbers are closed under addition (the sum of any two natural numbers is always a natural number). Are they closed under subtraction? Provide a couple of examples to justify your answer.[2]
13.Can you think of other way(s) to find a rational number between any two rational numbers?[2]
14.Find the values using suitable identities: (i) $17 \times 21$[2]
15.Represent the rational numbers $\dfrac{2}{3}$[2]
16.Find possible expressions for the length and breadth of each of the following rectangles whose areas are given by the following expressions in square units. (i) $25a^2 - 30ab + 9b^2$[2]
17.Show that if two such isosceles triangles (occurring in the previous question) have equal base length, they are congruent to each other.[2]
18.Ancient Indians used the joints of their fingers to count, a practice still seen today. Each finger has 3 joints, and the thumb is used to count them. How many can you count on one hand? How does this relate to the ancient base-12 counting systems?[2]
🔑 Show Answer Key — Set 1
- 1. $8\sqrt{2}$ cm.
- 2. $607$ is the 122nd term.
- 3. $35°$ .
- 4. Theorem 6 says that equal chords of a circle are equidistant from the centre. If two equal chords have length $2a$ in a circle of radius r, the perpendicular from the centre bisects each chord. For each chord, the distance d from the centre satisfies $d^2+a^2=r^2$ , so $d=\sqrt{r^2-a^2}$ . Since r and a are the same for both chords, their distances from the centre are equal.
- 5. (i) $\dfrac{7}{10}$ (ii) $\dfrac{29}{24}$ (iii) $-\dfrac{5}{14}$
- 6. (i) $9$ (ii) $4a^3-a^2+6$
- 7. They are prime numbers between 10 and 20. The next three primes after 19 are $23, 29, 31$ .
- 8. (i) The tree branches from Basket A to Apple or Orange, and from each of these to Banana or Mango. (ii) By fruit type, $S=\{(\text{Apple},\text{Banana}),(\text{Apple},\text{Mango}),(\text{Orange},\text{Banana}),(\text{Orange},\text{Mango})\}$ . (iii) $P(\text{Apple and Banana})=\dfrac{1}{3}\times\dfrac{1}{2}=\dfrac{1}{6}$ .
- 9. (i) $176$ cm (ii) $\dfrac{62500}{11}\approx 5682$ revolutions
- 10. (i) $\left(2y+\dfrac{1}{4y}\right)^2$ (ii) $\left(3m-\dfrac{1}{5n}\right)\left(3m+\dfrac{1}{5n}\right)$ (iii) $\left(3b-\dfrac{1}{4b}\right)\left(9b^2+\dfrac{3}{4}+\dfrac{1}{16b^2}\right)$ (iv) $\left(x+\dfrac{1}{2}\right)\left(x+\dfrac{1}{3}\right)$ (v) $\left(3u-\dfrac{1}{5}\right)^3$ (vi) $\left(4y+\dfrac{z}{5}\right)\left(16y^2-\dfrac{4}{5}yz+\dfrac{z^2}{25}\right)$ (vii) $(p+3q+r)(p^2+9q^2+r^2-3pq-3qr-pr)$ (viii) $(3m-2)^2$ (ix) $\dfrac{1}{3}(3x-2y+z)(9x^2+4y^2+z^2+6xy+2yz-3xz)$ (x) As printed, the $xy$ and $xz$ coefficients are interchanged from a perfect square. The intended expression $4x^2+9y^2+36z^2+12xy+36yz+24xz$ factors as $(2x+3y+6z)^2$ . (xi) $\left(3u-\dfrac{1}{6}\right)^3$
- 11. $0.\overline{9}=1$ .
- 12. No. Natural numbers are not closed under subtraction. For example, $5-2=3$ is natural, but $2-5=-3$ is not a natural number. Also, $4-4=0$ , and 0 is not a natural number in the usual NCERT convention $\mathbb{N}=\{1,2,3,\ldots\}$ .
- 13. Yes. One simple method is to take the average. For any two rational numbers $a$ and $b$ with $a\lt b$ , the number $\dfrac{a+b}{2}$ is rational and lies between them.
- 14. (i) $357$ (ii) $9984$ (iii) $384$ (iv) $3176523$ (v) $7880599$ (vi) $2048383$ (vii) $-1225043$ (viii) $-26730899$
- 15. $\dfrac{2}{3}$ lies between 0 and 1, two-thirds of the way from 0 to 1. $-\dfrac{5}{4}=-1.25$ lies between $-2$ and $-1$ . $\dfrac{11}{2}=5.5$ lies halfway between 5 and 6.
- 16. (i) Length $=5a-3b$ , breadth $=5a-3b$ . (ii) Length $=6s+7t$ , breadth $=6s-7t$ .
- 17. Let the two chords be AB and DE in the same circle with centre O, and suppose $AB=DE$ . Join OA, OB, OD and OE. Since all four are radii, $OA=OB=OD=OE$ . Also $AB=DE$ . Thus $\triangle AOB$ and $\triangle DOE$ have three corresponding sides equal, so they are congruent by SSS.
- 18. Using the thumb to count the three joints on each of the four fingers, one can count $4\times 3=12$ positions on one hand. This naturally supports counting in groups of 12, which is the idea behind base-12 systems.