$38.90 → 100% (always take the original as 100%)

Add 7% GST,

100% + 7% = 107%

Remember that 107% = 107/100 = 1.07

So cost including GST

= $38.90 × 107/100
= $41.623
≈ $41.62 (nearest cent)

Or

$38.90 × 1.07
= $41.623
≈ $41.62 (nearest cent)

Q6

$10000 is the principal amount. Interest rate is 2.6% per year.

So after 1 year,

100% + 2.6% = 102.6%
= 102.6 / 100
= 1.026

Now every year the interest earned is 2.6% of the new amount in the bank (which includes the previous years' interest)

Treat each year as a new 100%

So for 8 years, the working will simply be :

$10 000 × 1.026 × 1.026 × ... × 1.026
(8 '1.026's altogether)

Rewrite as:

$10 000 × (1.026)⁸

= $12 279.4492
≈ $12 279.45 (nearest cent)



Amount of interest earned
= $12 279.45 - $10 000 (initial deposit)
= $2 279.45