Let's call the bigger number n So the smaller number is 2/5n So n + 2/5n = 21 Which is equivalent of n + 2n/5 = 21 Then you need to get rid of the fraction by multiplying everything by 5 5n + 2n = 105 Or simply 7n = 105 Divide both sides by 7 to isolate n n = 15 So the larger number is 15 Now we need to work out 2/5 of 15 to work out the smaller number (15/5 [the denominator])*2 [the numerator] = 6 So the two numbers are 15 and 6