When the price of a toy was increased by 20%,the number of toys sold was decreased by 15%.What was its effect on the total sales of the shop?

$$ price of toys \times number of toys = total sales of the shop $$

Assume that initial price of the toy = 100

Assume number of toys = 100

then total sales = $$ 100 \times 100 = 100 $$

 price of a toy was increased by 20% , new price = $$ 100 \times \frac{120}{100} = 120 $$

number of toys sold was decreased by 15%, new number = $$ 100 \times \frac{85}{100} = 85 $$

then new sales = $$ 120 \times 85 = 10200 $$

effect on the total sales of the shop = $$ \frac{10200 - 10000}{10000} \times 100 = \frac{200}{10000} \times 100 = 2 $$

thus 2% increase