# Ncert Solutions For Class 7 Maths Ex 12.4

## Ncert Solutions For Class 7 Maths Chapter 12 Ex 12.4

Q1: Observe the pattern made from the line segment, which are of equal length which are found in display of calculators and digital speedometer: If n is the number of digits, and the number of required segments to form the digit n is given by the algebraic expression on the right of the digit. So how many segments are required to form 5,10,100 digits of the kind .

Sol:

S.no Symbols Digit’s number Pattern Formulae No. of segments
(i)

 5 10 100
5n+1$5n+1$

 26 51 501
(ii)

 5 10 100
3n+1$3n+1$

 16 31 301
(iii)

 5 10 100
5n+2$5n+2$

 27 52 502

(i) 5n+1$5n+1$

Putting n=5,          5×5+1=25+1=26$5\times 5+1=25+1=26$

Putting n=10,        5×10+1=50+1=51$5\times 10+1=50+1=51$

Putting n=100,       5×100+1=500+1=501$5\times 100+1=500+1=501$

(ii) 3n+1$3n+1$

Putting n=5,          3×5+1=15+1=16$3\times 5+1=15+1=16$

Putting n=10,        3×10+1=30+1=31$3\times 10+1=30+1=31$

Putting n=100,        3×100+1=300+1=301$3\times 100+1=300+1=301$

(iii) 5n+2$5n+2$

Putting n=5,          5×5+2=25+2=27$5\times 5+2=25+2=27$

Putting n=10,        5×10+2=50+1=52$5\times 10+2=50+1=52$

Putting n=100,       5×100+2=500+1=502$5\times 100+2=500+1=502$