Question

I.
Choose the correct option.
1.
The ratio of 4 km to 1800 m is
c. 20:9
d. 4:27
2.
a. 4:18
b. 9:20
1 1
in the lowest terms can be written as
20 30
a. 4:5
b. 2:3
c. 3:2
d. 20:30
3.
The fourth proportional to 10, 16 and 25 is
a.
1
b. 40
c. 31
d. 36
4.
What value of x will make 25, x and 9 in continued proportion?
a.
16
b. 17
c. 15
d. 11
5.
The mean proportional between 40 and 10 is
a. 20
b. 24
c. 25
d. 30​

Answer 1

Answer:

Ans 1) Ratio of 4 km to 1800 m

We know that Two things can only compared if their unit is same

so, we will convert both these to metre

4000 : 1800

= (c) 20 : 9 is correct option

Ans 2) 20:30 in the lowest term

= 2:3

So, (b) 2:3 is correct option

Ans 3) Let the fourth proportional be x

= 10:16 :: 25:x

⇒ Product of extreme terms = Product of mean terms

⇒10x = 16×25

⇒ x = 16×25/10

⇒ x = 16×5/2

⇒ x = 80/2

⇒ x = 40

Hence,the correct option is (b) 40

Ans 4) Since, 25, x , 9 are in proportion

⇒25, x , x , 9 are in proportion

⇒Product of extremes terms × Product of mean terms

⇒25 × 9 = x²

⇒x² = 25×9

⇒x² = 225

⇒x = √225

⇒x = 15

Hence, option (c)15 is correct

Ans 5) Let x be the mean proportional Between 40 and 10. Then,

⇒x² = 40×10

⇒x² = 400

⇒x = √400

⇒x = 20

Hence, option (a) 20 is correct

Hope it helps

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