S.chand publication New Learning Composite mathematics solution of class 7 Chapter 2 Fractions and Decimals Exercise 2M

 Exercise 2M

Question 1

Find in cm, the height of a pile of books is each is 2 cm 3 mm thick.

Sol :

2cm 3mm=(2×10)mm+3mm

=(20+3)mm=23mm

Height of a pile of 15 books=(23×15)mm

=345mm

Question 2

A pile of 160 sheets is 6.08 cm high. Find in mm the thickness of one sheet.

Sol :

6.08cm=(6.08×10)mm

=60.8mm

Thickness of one sheet$=\frac{60.8}{160}$mm

=0.38mm

Question 3

How many pieces of tape each 6 cm long, can be cut from a length of 1 m 5 cm and how much remains?

Sol :

1m5cm=(100+5)cm

=105cm

Pieces of tape can be cut$=\frac{105}{6}$cm

=17 cm and 8 cm remaining 

Ans: 17 pieces can be cut from tape and 3cm remaining

Question 4

How many jars each holding 1.75 kg of jam can be filled from a vessel containing 100 kg of jam and how much remains?

Sol :

Number of jars can be filled with jam$=\frac{100}{1.75}=\frac{10000}{175}$

=57 and 25 kg jam remaining

Ans: 57 jams can be filled with jam and 25kg jam remaining 

Question 5

A racing car travels 425 m in 10 sec; express this speed in km per hour.

Sol :

9m10sec a car travels 425m

1 sec a car travels $\frac{425}{10}$

3600 sec a car travels $\frac{425 \times 3600}{10}$m

=153000=153km

Ans: 153km/hour

Question 6

A flask weighs 64.27 g when empty and 150.35 g when full of water. Find its weight when it is half full of water.

Sol :

Weight of water=(150.35-64.27)g=86.08g

Weight of flask when it is half full of water

$=\left(64.27+\frac{86.08}{2}\right)$g

=(64.27+43.04)g

=107.31g

Question 7

A square and an equilateral triangle have a side in common. If a side of the triangle is 15 mm long, find the perimeter of the figure given alongside in cm.

Sol :

Perimeter of equilateral triangle=(15×3)mm

=15mm=45cm

Ans : Perimeter of triangle 45cm

Question 8

Diameter of Earth is 12756000 m. A new plant was discovered whose diameter 5/86 of the diameter of Earth. Find the diameter of the planet of this planet in km.

Sol :

Diameter of new planet$=12756000\times \frac{5}{86}$m

=741627.907m or 741.628km

Ans : Diameter of this planet is 741.628km

Question 9

Ravindra is 144 cm tall. That is 9/10 as tall as his elder brother. How tall is Ravindra’s elder brother?

Sol :

Height of rabindra's elder brother$=\left(144 \div \frac{9}{10}\right)$cm

$=144 \times \frac{10}{9}$cm

=160 cm

Question 10

A public sewer line is being installed along 161/2 m of road. The supervisor says that the labourers will be able to complete 7.5 m in one day. How long will the project take to complete?

Sol :

Labours able of complete 7.5m in 1day

Labours able of complete 1m in $\frac{1}{75}$day

Labours able of complete $80\frac{1}{2}$m in $=\frac{10}{7.5}\times 80\frac{1}{2}$day

$=\frac{10}{75}\times \frac{161}{2}$

=10.73≅11

Ans : The project will take 11 days to complete