Revision:Round off a whole number to a certain place valueEx: Round off 351 924 to the nearest

(a) thousand(b) ten thousand(c) hundred thousand

Answer:(a) 352 000(b) 350 000(c) 400 000

Significant figures- the number of digits in a number , in integer form or decimal form, which is

round off to a certain degree of accuracy.

Rules to be followed:Rules Examples(a) The non-zero digits in a positive number are significant figures.

23.7 (3 s.f.)1658 (4 s.f.)

(b) The zeros between the non-zero digits are significant figures.

50.8 (3 s.f.)700.01 (5 s.f.)

(c) The zeros after a non-zero digit in a decimal are significant figures.

4.10 (3 s.f.)690.0 (4 s.f.)

(d) The zeros before a non-zero digit in a decimal less than 1 are not significant figures.

0.025 (2 s.f.)0.00138 (3 s.f.)

(e) The zeros after a non-zero digit in a whole number may or may not be significant figures depending on the degree of accuracy.

398(i) If the degree of accuracy is to the nearest hundred

398 = 400 (1 s.f.)(ii) If the degree of accuracy is to the nearest ten. 398 = 400 (2 s.f.)

Exercise:1. State the number of significant figures.

(a) 438(b) 40308(c) 7.060(d) 0.0068(e) 0.508

2. Round off the following and correct to the number of significant figures stated in the brackets.

(a) 2349 [2](b) 5068 [2]

(c) 6950 [2](d) 0.2988 [3](e) 0.006749 [2](f) 0.0805 [2](g) 0.082995 [4](h) 9.474 [3](i) 387.57 [3](j) 49.56 [1](k) 2.9876 [2]

Addition, subtraction, multiplication and division involving a few numbers and state the answer in specific significant figures.Example:Solve each of the following and correct your answer to three significant figures.(a) 468 ÷ 3 – 0.068(b) 4.25 ÷ 005 × 35(c) (253.12 – 57.9)× 15(d) 1.33×0.25+8.94÷20(e) 4.5+0.69×7.96-3.1

Solving problems involving significant figuresEx 1:A rectangular field is 2.25 km long and 1.35 m breadth. Find the area of the field and round off your answer to the three significant figures.

Ex 2: The diameter o a sphere is 12 cm. Calculate the volume, in cm3, of the sphere. Round off your answer to three significant figures.

[Given volume of sphere = and use ]