Question

a ÷ 100 ÷ 10 x 3 + 390 = 510

Answer 1

$a \div 100 \div 10 \times 3 + 390 = 510$

$\frac{1}{100}a \times \frac{1}{10} \times 3 + 390 = 510$

$\frac{3}{1000}a + 390 = 510$

$3a + 390000 = 510000$

$3a = 510000 - 390000$

$3a = 120000$

$a = 40000$