Selina solutions

Selina solutions

Selina solutions

Grade 7

CHAPTERS

3. Fractions (Including Problems)

4. Decimal Fractions (Decimals)

5. Exponents (including Laws of Exponents)

6. Ratio and Proportion (Including Sharing in a Ratio)

7. Unitary Method (including Time and Work)

11. Fundamental Concepts (Including Fundamental Operations)

12. Simple Linear Equations (Including Word Problems)

13. Set Concepts (Some Simple Divisions by Vedic Method)

14. Lines and Angles (Including Construction of angles)

17. Symmetry (Including Reflection and Rotation)

18. Recognition of Solids (Representing 3-D in 2-D)

Q12) The mean of six numbers :x-5,x- 1, x, x + 2, x + 4 and x + 12 is 15. Find the mean of first four numbers.

Solution:

The mean of six numbers are x – 5, x – 1, x, x + 2, x + 4 and x + 12 is 15

Mean=\frac{Sumofallobservations}{No.ofobservations}

Mean=\frac{((x-5)+(x-1)+(x)+(x+2)+(x+4)+(x+12))}{6}

=\frac{(x-5+x-1+x+x+2+x+4+x+12)}{6}

=\frac{(12+6x)}{6}=15

12 + 6x = 90

6x = 90 – 12

6x = 78

x=\frac{78}{6}=13

x = 13

∴ The six numbers are (13 – 5), (13 – 1), 13, (13 + 2), (13 + 4), (13 + 12) i.e. 8, 12, 13, 15, 17, 25

Now, mean of first four numbers = \frac{(8+12+13+15)}{4}=\frac{48}{4}=12

Still have questions? Our expert teachers can help you out

Book a free class nowFractions (Including Problems)

Exponents (including Laws of Exponents)

Ratio and Proportion (Including Sharing in a Ratio)

Unitary Method (including Time and Work)

Fundamental Concepts (Including Fundamental Operations)

Simple Linear Equations (Including Word Problems)

Set Concepts (Some Simple Divisions by Vedic Method)

Lines and Angles (Including Construction of angles)

Symmetry (Including Reflection and Rotation)

Recognition of Solids (Representing 3-D in 2-D)

Solution:

The mean of six numbers are x – 5, x – 1, x, x + 2, x + 4 and x + 12 is 15

Mean=\frac{Sumofallobservations}{No.ofobservations}

Mean=\frac{((x-5)+(x-1)+(x)+(x+2)+(x+4)+(x+12))}{6}

=\frac{(x-5+x-1+x+x+2+x+4+x+12)}{6}

=\frac{(12+6x)}{6}=15

12 + 6x = 90

6x = 90 – 12

6x = 78

x=\frac{78}{6}=13

x = 13

∴ The six numbers are (13 – 5), (13 – 1), 13, (13 + 2), (13 + 4), (13 + 12) i.e. 8, 12, 13, 15, 17, 25

Now, mean of first four numbers = \frac{(8+12+13+15)}{4}=\frac{48}{4}=12

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Book a free class nowLido

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