Multipliers and Interest

Write down the decimal multiplier for:
(a) an increase of $\displaystyle 3.4\%$
(b) a decrease of $\displaystyle 2.75\%$

$\displaystyle \pounds 3800$ is deposited in an account with an effective rate of interest of $\displaystyle 2.6\%$ per year.
Calculate the value of the account after $\displaystyle 1$ year.

$\displaystyle \pounds 9200$ is invested in an account with an effective rate of interest of $\displaystyle 3.15\%$ per year.
Calculate the value of the investment after $\displaystyle 4$ years.
Give your answer to the nearest penny.

An investment of $\displaystyle \pounds 7500$ grows by $\displaystyle 4.2\%$ in the first year and then by $\displaystyle 1.9\%$ in the second year.
Calculate its value after $\displaystyle 2$ years.
Give your answer to the nearest penny.