7*0.23 =1.61 pints of alcohol in 7 pints of 23% solution
3*0.7 =2.1 pints of alcohol in 3 pints of 70% solution
10x = pints pf alcohol in 10-pint mixture
7*0.23+3*0.7=10x
1.61+2.1=10x
3.71 = 10x
x = 0.371 = 37.1% is the concentration of the new 10-pint mixture
