Find 5 rational numbers between 25 and 35.
Answer: Multiply top and bottom by 6: 1230 and 1830. Five numbers between: 1330, 715, 12, 815, 1730.
Step-by-step solution
Idea: The numerators 2 and 3 have no whole number between them. Multiply top and bottom by 5 + 1 = 6 to make room for exactly 5.
- 25 = 2 × 65 × 6 = 1230 and 35 = 1830.1 mark
- Numerators 13, 14, 15, 16, 17 lie between: 1330, 1430 = 715, 1530 = 12, 1630 = 815, 1730.1 mark
13/30, 7/15, 1/2, 8/15 and 17/30 (other correct sets exist, e.g. 0.41, 0.45, 0.5, 0.55, 0.59).
Check: Decimals: 0.4 < 0.433 < 0.467 < 0.5 < 0.533 < 0.567 < 0.6 ✓.
Answer to write in the exam
25 = 1230, 35 = 1830
∴ Five rational numbers: 1330, 1430, 1530, 1630, 1730 (= 1330, 715, 12, 815, 1730)
Common mistakes that cost marks
- Multiplying only the numerators by 6.
- Giving 2.55 as an answer. Its value (12) is between, but in the form pq both p and q must be integers: write 510 or 12.
- Multiplying by 5 instead of 6, which gives only 4 numbers between (1125 to 1425).
How this can come in the exam
MCQ (1 mark)
A rational number between 37 and 47 is
- 714
- 314
- 914
- 414
Show answer
(A) 714
614 < 714 < 814.
Short answer (2 marks)
Find three rational numbers between 14 and 12.
Show answer
14 = 416 and 12 = 816 (1 mark). 516, 616 = 38, 716 (1 mark).Try one yourself
Find 3 rational numbers between 49 and 59.
Show answer
×4: 1636 and 2036 → 1736, 1836 = 12, 1936.
More questions like this
- Find 5 rational numbers between 16 and 25.
- If x3 + x5 = 1615, find the rational number x.
- Let a and b be two non-zero rational numbers such that a + 1b = 0. Without assigning any numerical values, determine whether ab is positive or negative. Justify your answer.
- A rational number has a terminating decimal expansion whose last non-zero digit occurs in the 4th decimal place. Show that such a number can be written in the form p104, where p is an integer not divisible by 10. Is it necessary that the denominator of this rational number, when written in the lowest form, is divisible by 24 or 54? Give reasons.
- Without performing division, determine whether the decimal expansion of 18125 is terminating or non-terminating. If it terminates, state the number of decimal places.