Test: Decimals - JAMB MCQ

Formula used:

Calculation:

By using the above formula

Alternate Method
Calculation:

By subtracting eq.1 from eq.2: 

99x = 122

⇒ x = 122/99

By subtracting eq.3 from eq.4:

99y = 86

⇒ y = 86/99

By subtracting eq.5 from eq.6:

99z = 29

⇒ z = 29/99

Given:

 {(.98)3 + (0.02)3 + 3 × 0.98 × 0.02 – 1}

Concept used:

(a + b)3 = a3 + b3 + 3ab(a + b)

Calculation:

{(.98)³ + (0.02)³ + 3 × 0.98 × 0.02 – 1

⇒ [(.98)³ + (0.02)³ + 3 × 0.98 × 0.02(0.98 + 0.02)} – 1]

Now, first term is of the form (a + b)3 where a = .98 and b = 0.02

⇒ (0.98 + 0.02)³ – 1 = 1 – 1 = 0

∴ The value is 0.

Mistake Points:

In this type of question, in the numerator, there are 6.75 and 4.25, while in the denominator there is 67.5, and 42.5 is present in multiplication.

From the denominator, we can write 67.5 × 67.5 as 6.75 × 10 × 6.75 × 10 = 100 × (6.75), and similarly for other terms.

Therefore we take 100 as common from the denominator.

Identity used:

a³ - b³ = (a - b) (a² + b² + ab)

Calculation:

⇒ ? = 2.5/100

⇒ ? = 0.025

∴ ? = 0.025

Given expression is,

⇒ (?)³ × 10 = 13230 ÷ (9.261 ÷ 7)

⇒ (?)³ × 10 = 13230 ÷ (1.323)

⇒ (?)³ × 10 = 10000

⇒ (?)³ = 1000

⇒ (?)³ = (10)³

⇒ ? = 10

Since,

a² - b² = (a - b) ( a + b)

⇒ 0.9 × 0.7 = 0.63

∴ Answer is 0.63

⇒ 0.2689 × 10000

⇒ 2689

Hence the correct answer is "2689".

⇒ [ ( 0.75 × 0.75 × 0.75 ) / 0.25 ] + [ 1.75 + 0.5625 ]

⇒ [ ( 3 × 0.5625 ) ] + [ 2.3125 ]

⇒ [ 1.6875 + 2.3125 ]

⇒ 4

Now √4 = 2 

Hence the correct answer is "2".

Given:

Concept used:

a² - b² = (a + b) × (a - b)

Calculation:

⇒ [(4.2² - 1.9²) + 2.3]/(2.3 × 7.1) = ?

⇒ [(4.2 + 1.9) × (4.2 - 1.9) + 2.3]/((2.3 × 7.1) = ?

⇒ (2.3 × 6.1 + 2.3)/(2.3 × 7.1) = ?

⇒ 2.3 × (6.1 + 1)/(2.3 × 7.1) = ?

⇒ (2.3 × 7.1)/(2.3 × 7.1) = ?

? = 1

Calculation:

Let x = 0.0181818....

⇒ 10x = 0.1818.... ----eq (1)

⇒ 1000x = 18.1818.... ----eq (2)

Now, eq (2) - eq (1)

⇒ 1000x - 10x = 18.1818... - 0.1818...

⇒ 990x = 18

⇒ x = 18/990

⇒ x = 1/55
∴ The fraction of  is 1/55

0.36 of 52.5 + ? of 35 = 57.4

⇒ 18.9 + ? of 35 = 57.4

⇒ ? of 35 = (57.4 − 18.9)

⇒ ? = 38.5/35 

⇒ ? = 1.1

1132.757 – 2315.996 – 1753.829 + 2 × 2846.639

= 1133 – 2316 – 1754 + 5694

= (1133 + 5694) – (2316 + 1754 )

= 6827 – 4070

= 2757

Given expression,

(81.84 + 118.16) ÷ 5³ = 1.2 × 2 + ?

⇒ 200 ÷ 5³ = 1.2 × 2 + ?

⇒ 200 ÷ 125 = 1.2 × 2 +?

⇒ 1.6 = 2.4 + ?

⇒ ? = -0.8

0.3333 × 0.25 × 0.499 × 0.125 × 24

⇒ 1 / 3 × 1 / 4 ×  499/1000 × 1/8 × 24

⇒ 1 /3 × 1 / 4 × 499 / 1000 × 3

⇒  1 / 4 × 499 / 1000

⇒  499/4000

⇒  0.12475 ~ 0.125

⇒  0.125 = 1/8

Hence the correct answer is "1/8".

Given:

Largest decimal number.

Calculations:

From the given facts, 18.8 is the largest decimal number out of rest given options as, in the rest three options after the decimal point there are zeros making the number smaller than 18.8

∴ The answer is 18.8.

(0.009 ÷ ?) + (0.007 ÷ 0.07) + (0.04 ÷ 0.4) = 0.3

⇒ ? = 0.009 × 10

⇒ ? = 0.09

∴ The value of "?" is 0.09