SECTION D - MATHEMATICS The average age of a group of 25 girls is 10 years. If one gin
aged 12 years and 4 months joins the group, find, correct to one
decimal place, the new average age of group.
10.1 years (b) 9 3 years (c)8.7 years (d) 8.3 years

first one because it can't have a fraction in it

step-by-step explanation:

12

step-by-step explanation:

12 + 5 = 17

12x2=24

24-7=17

the solution of the equation is 2.23 ⇒ answer b

step-by-step explanation:

* lets revise the meaning of exponential function

- the form of the exponential function is y = ab^x, where a ≠ 0, b > 0 ,  

  b ≠ 1, and x is any real number

- it has a constant base b

- it has a variable exponent x

- to solve an exponential equation, take the log or ln of both sides,  

  and solve for the variable

* lets solve the problem

∵

- the base is 7 and the exponent is x

- insert ㏑ in both sides

∴

- use the rule

∴ x ㏑(7) = ㏑(77)

- to find x divide both sides by ㏑(7)

∴

* the solution of the equation is 2.23 to the nearest 2 decimal places